UC-NRLF 


COMBUSTION  AND 
SMOKELESS  FURNACES 


JOS.  W,  HAYS 

COMBUSTION  ENGINEER 


COMBUSTION  AND 
SMOKELESS   FURNACES 


JOS.  W.  HAYS 

COMBUSTION   ENGINEER 
CHICAGO,  U.  S.  A. 

SECOND   EDITION   (REVISED) 


PRICE  TWO  DOLLARS  PER  COPY 


JOS.  W.  HAYS,  Publisher 

ROGERS   PARK,    CHICAGO,   U.  S.  A. 

1915 


Copyright  1915 

by 
JOS.  W.  HAYS 


PREFACE 

THERE  has  long  been  need  of  a  practical  and  comprehensive 
work  on  Combustion  as  related  to  the  efforts  being  made  every- 
where to  secure  smoke  abatement.  Muoh  has  been  written  upon 
the  subject  in  works  devoted  to  general  engineering,  and  a  great 
deal  is  to  be  found  in  periodical  literature.  These  sources  of 
information  are  so  scattered,  and  each  in  itself  so  incomplete, 
that  the  average  person  is  barred  by  lack  of  time  and  library 
facilities  from  making  such  an  examination  as  would  enable  him 
to  arrive  at  a  clear  understanding  of  the  subject  in  all  its  bearings. 

This  work  is  designed  to  meet  what  the  author  believes  to  be 
the  needs  of  those  most  directly  interested  in  "  Smokeless  Fur- 
naces"—  the  owners  and  engineers  of  steam  power  plants.  It 
is  too  often  the  case  that  the  most  ignorance  prevails  where  the 
broadest  knowledge  should  be  found.  More  examples  of  this 
fact  are  probably  to  be  found  among  individuals  directly  concerned 
with  the  boiler  room,  than  any  other  class.  Crimes  are  com- 
mitted against  the  boiler,  the  counterpart  of  which,  if  enacted 
in  any  other  part  of  the  plant,  would  call  down  the  wrath  of  every- 
body either  directly  or  remotely  connected  with  the  institution. 

The  general  public  are  interested  in  the  furnace  and  boiler. 
The  chimney  furnishes  the  bond  of  interest.  One  writer  with  a 
penchant  for  statistics  estimates  that  a  damage  aggregating 
$40,000,000  per  annum  is  caused  by  the  smoking  chimneys  of 
Chicago.  These  astounding  figures  may  be  the  result  of  an  in- 
flamed imagination,  but  the  fact  remains  that  the  damage  is 
tremendous.  The  movement  against  the  smoke  nuisance  is 
attaining  formidable  proportions,  and  radical  reforms  in  the 
larger  centers  of  population  cannot  be  much  longer  procrastinated. 

The  owner  and  engineer  desiring  to  institute  reforms  in  order 
to  secure  increased  furnace  efficiency,  or  satisfy  the  demands 
of  the  smoke  inspector,  are  confronted  with  what  is  often  a  puz- 
zling and  annoying  problem.  That  this  problem  is  too  often 
incorrectly  solved,  the  unscientific  and  archaic  devices  installed 

iii 


S3S477 


iv  PREFACE 

under  thousands  of  boilers  to  secure  smoke  abatement  will  bear 
witness. 

If  this  volume  will  help  to  a  better  understanding  of  Com- 
bustion, and  how  to  attain  it  in  a  scientific  and  practical  manner 
in  a  steam  boiler  furnace,  it  will  then  have  well  served  its  pur- 
pose. Proper  original  design  and  installation  are  of  extreme 
importance,  but  these  matters  cannot  be  treated  in  this  work. 
To  dismantle  a  power  plant,  and  reconstruct  it  along  correct  lines, 
is  only  occasionally  a  feasible  proposition.  The  owner  is  usually 
forced  to  accept  the  main  features  of  a  bad  situation,  and  make 
only  such  minor  and  inexpensive  changes  and  improvements  as 
his  circumstances  will  allow.  This  work  is  intended  to  help  the 
owner  and  engineer  to  rational  conclusions  as  to  feasible  devices 
and  improvements,  and  to  enable  them  to  differentiate  between 
the  practical  " Smokeless  Furnace"  and  the  impractical  "cure- 
all"  that  had  its  origin  in  the  nightmares  of  some  crazy  inventor. 
Nearly  1500  United  States  patents  are  to-day  in  force  on  boiler 
furnace  devices.  Hundreds  of  these  devices  are  of  such  a  nature 
as  to  amply  justify  the  language  above  used. 

Technical  terms  and  formulae  will  be  avoided  throughout  the 
work  as  far  as  possible,  —  the  aim  being  to  present  the  subject 
in  such  form  that  the  layman,  and  the  man  of  limited  experience 
with  boiler  plants,  will  be  able  to  comprehend  it.  A  list  of  the 
authorities  drawn  upon  in  the  preparation  of  the  book  will  be 
found  appended. 

Jos.  W.  HAYS. 

CHICAGO,  January  10,  1906 


Revised  March  22,  1915. 


AUTHORITIES   CITED 

The  following  authorities  have  been  consulted  and  drawn  upon 
in  the  preparation  of  this  work:  — 

The  various  works  of  Prof.  R.  H.  Thurston,  Wm.  M.  Barr,  Sir  Robert  Kane 

and  Sir  Humphrey  Davy. 
Daniel  Kinnear  Clark,  "The  Steam  Engine." 
William  Kent,  "Steam  Boiler  Economy." 
Peabody  and  Miller,  "The  Steam  Boiler." 
Prof.  Rankine,  "Manual  of  the  Steam  Engine." 
Williams,  "Fuel,  Its  Combustion  and  Economy." 
Pullem,  "Combustion  and  Smoke  Prevention." 
Nicholson,  "Combustion." 

M.  Scheurer  Kestner,  "Etudes  sur  la  Combustion  de  la  Huille." 
Sir  Wm.  Fairbairn,  "Report  of  British  Association." 
Encyclopedia  Britannica,  "Heat  and  Combustion." 
Engineering  Magazine,  Vol.  XXII,  p.  924,  "Smoke  Abatement." 
C.  A.  Benjamin,  in  Current  Literature,  Vol.  XXXII,  p.  419,  "Smoke  Abate- 
ment in  Cleveland." 

Outlook,  February,  1902,  "Smoke  Abatement  in  Large  Cities." 
Outlook,  June,  1902,  "The  Smoke  Nuisance  in  New  York." 
Engineering  Magazine,  Vol.  XXIV,  p.  280,  "Purifying  the  Atmosphere  of 

Towns  and  Cities." 

Review  of  Reviews,  July,  1903,  "The  Smoke  Nuisance  in  Industrial  Centres." 
Dublin  Review,  "Vol.  CXIV,  p.  225,  "Smokeless  Combustion." 
Journal  of  the  Franklin  Institute,  Vol.  CXLIII,  p.  393;  Vol.  CXLIV,  pp.  17 

and  401;  Vol.  CXLV,  p.  1,  "The  Smoke  Nuisance  and  Its  Regulation." 
W.  H.  Bryan,  Cassier's  Magazine,  Vol.  XIX,  p.  17,  "Smoke  Abatement." 
Cassier's  Magazine,  Vol.  XX,  p.  129,  "Smoke  from  a  Great  City." 
R.  H.  Thurston,  Science,  Vol.  IX,  p.  55,  "The  Suppression  of  Smoke." 
F.  H.  Mason,  American  Architect,  Vol.  LXV,  p.  38,  "Smoke." 
Nature,  Vol.  XXIII,  p.  48,  "The  Smoke  Nuisance." 

Chambers'  Journal,  Vol.  XIX,  p.  245,  "The  Smoke  Nuisance,  —  Is  It  Cur- 
able?" 

Eclectic  Engineering  Magazine,  Vol.  VIII,  p.  209,  "Smoke  Prevention." 
Sir.  F.  Pollock,  Nineteenth  Century  Magazine,  Vol.  IX,  p.  478,  "Smokeless 

Combustion." 

J.  C.  McDakin,  Eclectic  Engineering  Magazine,  Vol.  VII,  p.  528. 
Siemans,  Nature,  Vol.  XXIII,  p.  25,  "Smoke  Prevention." 
W.  F.  Pollock,  American  Architect,  Vol.  IX,  p.  151,  "Smoke  Prevention." 
J.  W.  Hill,  Eclectic  Engineering  Magazine,  Vol.  XXII,  p.  82,  "Smoke  Pre- 
vention." 


vi  AUTHORITIES    CITED 

W.  Woodcock,  Journal  of  the  Franklin  Institute,  Vol.  LIX,  p.  84,  "Smoke 

Prevention." 
W.  D.  S.  Moncrieff,  Eclectic  Engineering  Magazine,  Vol.  XXIV,  p.  458,  "Smoke 

Prevention  in  London." 

Douglas  Galton,  Art  Journal,  Vol.  XXXIV,  p.   104,   "Smoke  Consuming 

Appliances." 
W.  Bonfield,  Art  Journal,  Vol.  XXXIV,  p.  9,  "Smoke  in  Manufacturing 

Districts." 

R.  S.  G.  Paton,  Kansas  City  Review,  Vol.  VII,  p.  477,  "The  Smoke  Nuisance." 
C.  W.  Williams,  Journal  of  the  Franklin  Institute,  Vol.  LXI,  p.  67,  "Smoke." 
American  Architect,  Vol.  XVII,  p.  305,  "The  Smoke  Nuisance." 
Journal  of  the  Franklin  Institute,  Vol.  LXI,  p.  126,  "Smoke  Burning." 
Chambers'  Journal,  Vol.  XXIX,  p.  234,  "Williams'  Plan  of  Smoke  Burning." 
Chambers'  Journal,  Vol.  LI,  p.  474,  "Smoke  Doctoring." 
Chambers'  Journal,  Vol.  XXI,  p.  201,  and  Vol.  XXVII,  p.  46,  "The  Smoke 

Nuisance." 

Gentlemen's  Magazine,  Vol.  XLIX,  p.  21,  "Smoke  in  London." 
W.  F.  Sicard,  Journal  of  the  Franklin  Institute,  Vol.  CXXXVIII,  p.  58,  "  Smoke 

Preventing  Appliances." 

Chambers'  Journal,  Vol.  XXIV,  p.  174,  "Smoke  Burning  and  Pure  Air." 
Rollo  Russell,  Nature,  Vol.  XXXIX,  p.  25,  "The  Prevention  of  Smoke." 
E.  Carpenter,  McMillan's  Magazine,  Vol.  LXII,  p.  204,  "The  Smoke  Plague 

and  Its  Remedy." 

Prof.  Rucker,  American  Architect,  Vol.  XI,  p.  283,  "The  Abatement  of  Smoke." 
W.  H.  Bryan,  Engineering  Magazine,  February,  1904,  "Smoke  Prevention." 
W.  C.  Popplewell,  "The  Prevention  of  Smoke." 
E.  W.  Dimond,  "Chemistry  of  Combustion." 
Hubert  Fletcher,  "The  Smoke  Nuisance." 
T.  Patterson,  "Abolition  of  Smoke  from  Steam  Boilers." 
Prof.  Frederick  R.  Button,  "Heat  and  Heat  Engines." 
Walter  B.  Snow,  "Steam  Boiler  Practice." 
Prof.  Jamieson,  "Steam  and  Steam  Engines." 


CONTENTS 

CHAPTER   I 
HEAT  AND  COMBUSTION 1 

CHAPTER   II 
COMBUSTION  AND  THE  BOILER  FURNACE 12 

CHAPTER  III 
COMBUSTION  AND  THE  STEAM  BOILER        36 

CHAPTER   IV 
THE  CHIMNEY  EVIL 41 

CHAPTER   V 
SMOKELESS  FURNACES  IN  GENERAL 56 

CHAPTER   VI 
MECHANICAL  STOKERS 61 

CHAPTER   VII 
HAND-FIRED  FURNACES 67 

CHAPTER   VIII 
SOME  CONCLUSIONS 96 


CHAPTER  I 

HEAT    AND    COMBUSTION 

A  CLEAR  understanding  of  the  laws  governing  combustion, 
and  especially  of  such  manifestations  of  these  laws  as  are  apparent 
in  the  furnaces  of  steam  boilers,  must  be  arrived  at  before  enter- 
ing upon  a  discussion  of  " Smokeless  Furnaces." 

''Combustion"  may  be  defined  as  the  chemical  union  of  com- 
bustible matter  with  oxygen,  "the  supporter  of  combustion." 
Oxygen  is  a  chemical  element.  In  its  free  state  it  occurs  as  a 
gas.  It  is  found  in  the  air  in  mechanical  union  with  nitrogen, 
and  in  water  in  chemical  union  with  hydrogen.  It  is  important 
to  distinguish  between  " mechanical"  and  "chemical"  union. 
Mechanical  union  is  simply  a  mixture  of  elements.  Chemical 
union  is  a  combination  or  fusion  of  elements  having  an  affinity 
for  each  other,  in  such  manner  that  a  substance  is  created  pos- 
sessing few  or  none  of  the  peculiarities  of  the  individual  elements. 
It  requires  more  or  less  energy  to  separate  elements  chemically 
combined.  Little  or  no  energy  is  required  to  separate  elements 
mechanically  combined.  Hence  it  follows  that  the  oxygen  of 
the  air  is  substantially  free  to  combine  with  the  carbon  contained 
in  coal,  while  the  oxygen  contained  in  water  or  carbonic  acid  gas 
is  not  free  to  enter  into  such  combination.  Apply  air  to  the 
furnace  fires  and  combustion  flourishes,  —  apply  water  or  car- 
bonic acid  gas  and  combustion  ceases. 

HEAT   THEORIES 

Heat  in  some  degree  always  accompanies  chemical  combina- 
tion, and  combustion  being  a  chemical  reaction,  heat  is  developed. 
What  is  heat?  This  apparently  commonplace  question  has 
puzzled  scientists  for  ages.  The  answer  is  still  shrouded  in  more 
or  less  mystery  and  theory.  In  many  of  the  familiar  phenomena 
which  are  accepted  by  the  common  run  of  humanity  without 
thought,  the  scientist  finds  his  greatest  problems.  Why  does 

l 


2  COMBUSTION   AND  SMOKELESS   FURNACES 

the  apple  fall?  The  world  had  been  satisfied  with  the  mere  fact 
that  it  did  fall,  until  it  occurred  to  Newton  to  inquire  why.  The 
theory  of  gravitation  advanced  astronomy  further  in  one  day 
than  it  had  progressed  in  all  the  preceding  centuries.  Who  shall 
say  what  potentialities  are  hidden  in  the  still  unsolved  questions 
concerning  heat,  and  its  cousin,  electricity?  We  know  that  when 
some  of  these  questions  are  answered  the  world  will  get  its  power, 
its  light  at  night  and  its  warmth  in  winter  direct  from  the  energy 
stored  in  the  coal.  When  that  time  arrives  there  will  no  longer 
be  a  "smoke  nuisance,"  —  furnaces  and  boilers  will  be  things 
of  the  past  and  found  only  in  museums  where  they  will  serve  as 
object  lessons  of  the  world's  progress. 

We  cannot  pass  without  some  notice  of  the  theory  of  heat. 
Newton  applied  himself  to  the  question,  "What  is  heat?"  He 
believed  it  to  be  some  form  of  energy  or  motion;  but  his  scientific 
mind  was  not  satisfied  to  the  point  of  putting  forth  any  such 
definite  theories  as  in  the  case  of  gravitation.  Bacon  held  in  a 
measure  to  the  same  views.  They  are  credited  by  modern  scien- 
tists with  being  nearer  to  the  truth  than  the  investigators  who 
immediately  followed  them. 

The  doctrine  that  "Heat  is  a  form  of  matter,"  a  mysterious 
and  subtle  elastic  fluid,  which  was  termed  "caloric,"  permeating 
the  pores  or  interstices  of  material  substances,  came  in  time  to 
be  generally  accepted.  Professor  Black,  of  the  University  of 
Glasgow,  was  the  chief  exponent  of  this  theory,  and  he  had  a 
numerous  following  among  scientists. 

Rumford  in  1798  and  Davy  in  1799,  by  their  experiments, 
completely  exploded  the  "material  theory"  of  heat.  The  now 
universally  accepted  "kinetic,"  or  "mechanical,"  or  "dynamic" 
theory,  as  it  is  variously  called,  grew  out  of  these  experiments. 
This  theory  was  further  advanced  by  Dr.  Mayer  of  Germany  in 
1842,  and  other  contemporaneous  investigators,  but  it  remained 
for  Dr.  Joule  of  Manchester,  in  1843,  to  secure  its  definite  and 
general  acceptance.  Joule  received  powerful  support  in  the  cele- 
brated Sir.  William  Thompson. 

Rumford  observed  that  heat  was  developed  by  the  boring 
out  of  a  cannon,  and  he  reasoned  that  as  heat  was  developed  by 
friction,  therefore  heat  must  be  some  form  or  mode  of  motion. 

Davy  had  arrived  at  the  same  conclusions,  which  were  strength- 
ened by  his  well-known  experiments  with  the  ice  cakes.  These 


HEAT  AND  COMBUSTION  3 

experiments  were  conducted  in  a  room  which  was  at  a  tempera- 
ture of  29  deg.,  or  3  deg.  below  the  freezing  point.  Two  flat 
cakes  of  ice  were  rubbed  together  with  some  force,  and  it  was 
noticed  that  the  ice  melted  at  the  point  of  contact  and  that  the 
temperature  of  the  water  produced  was  35  deg. 

Since  Joule  and  Thompson,  it  has  been  universally  accepted 
that  matter  is  composed  of  infinitesimal  particles  in  a  state  of 
motion,  and  that  friction  and  heat  result.  It  was  fully  fifty 
years,  however,  after  Davy  announced  his  experiments  and  con- 
clusions, before  the  scientific  world  was  fully  ready  to  accept 
the  new  theory.  The  "  materialistic "  school  held  stubbornly 
to  its  old  dogmas.  In  explaining  away  Davy's  experiments  it 
was  advanced  that  the  rubbing  together  of  the  ice  cakes  resulted 
in  "squeezing  out"  a  quantity  of  the  heat  fluid  or  " caloric"  as 
it  was  termed,  and  that  this  accounted  for  the  increased  temper- 
ature of  the  resulting  water.  The  champions  of  the  new  theory 
replied  to  this  argument,  "If  this  explanation  is  correct,  then 
it  follows  that  all  the  heat  fluid  may  be  expelled  from  a  substance 
if  a  sufficient  amount  of  friction  is  applied.  This  should  result 
in  lowering  the  temperature  of  the  substance  to  a  point  where 
it  might  profitably  be  employed  as  a  freezing  agency.  Reduce 
some  substance  to  this  condition,  and  we  will  abandon  the  new 
theory  for  the  old  one." 

Very  little  has  been  added  to  our  knowledge  concerning  the 
nature  of  heat,  since  1850.  "Heat  is  a  form  or  mode  of  motion." 
"Heat  is  something  communicable  from  one  body  to  another." 
We  must  be  satisfied  with  these  rather  hazy  and  indefinite  defini- 
tions, until  the  researches  of  some  scientist  shed  further  light 
upon  the  subject. 

A  great  deal  has  been  learned,  however,  about  the  properties 
of  heat,  and  some  notice  of  its  various  properties  and  peculiarities 
is  necessary  to  the  purposes  of  this  work. 

Distinction  must  be  made  between  the  terms  "heat"  and 
"temperature."  In  ordinary  speech  they  are  employed  more 
or  less  synonymously,  but  incorrectly  so.  By  "temperature" 
we  mean  the  "degree  of  heat."  "Cold"  is  a  purely  relative  term. 
We  say  that  a  thing  is  "hot,"  when  it  manifests  an  unusual  degree 
of  heat.  We  say  that  a  thing  is  "cold"  when  it  manifests  an 
unusual  lack  of  heat.  There  is  no  point,  strictly  speaking,  at 
which  heat  ceases  and  cold  begins.  There  is  such  a  point  upon 


4  COMBUSTION   AND   SMOKELESS   FURNACES 

the  scale  of  the  thermometer,  but  it  is  purely  arbitrary  and  serves 
the  purpose  of  harmonizing  the  thermometric  scale  with  the 
popular  ideas  of  heat  and  cold.  If  we  are  to  consider  temperature 
from  a  purely  scientific  standpoint,  the  real  "zero"  —  the  point 
where  heat  actually  begins  —  is  far  below  the  zero  of  the  ther- 
mometer. Heat  is  due  to  the  motion,  and  consequent  friction 
resulting,  of  the  particles  or  molecules  of  matter.  Now  there 
must  be  a  point  at  which  this  motion  reaches  its  minimum,  or, 
perhaps,  actually  ceases  altogether.  At  this  point,  what  we  call 
"cold"  ceases,  —  it  cannot  get  any  colder,  —  and  heat  has  its 
origin  or  beginning.  This  point  has  been  definitely  fixed  by  care- 
ful scientific  calculations.  It  is  492.66  deg.  below  the  freezing 
point  of  the  Fahrenheit  scale,  and  273.7  deg.  below  the  zero  of 
the  Centigrade.  It  is  known  as  the  "  absolute  "  or  true  zero  of 
heat  energy. 

If  the  molecules  of  matter  have  their  minimum  speed  of  mo- 
tion, then  it  is  reasonable  to  suppose  that  they  also  have  their 
maximum  speed.  What  is  the  greatest  degree  of  heat  possible? 
How  hot  is  it  when  it  cannot  get  any  hotter?  Science  has  figured 
this  out  to  the  last  degree,  largely  by  the  aid  of  mathematics 
based  upon  the  laws  of  gravitation.  The  highest  temperature 
that  man  has  been  able  to  produce  and  record  is  in  the  neighbor- 
hood of  5000  deg.  This  is  as  nothing  compared  with  the  pos- 
sibilities that  are  summed  up  in  heat.  If  a  mass  of  matter,  a 
stone  for  instance,  is  dropped  to  the  earth  from  a  height  of  say 
100  ft.,  it  will  have  developed  at  the  instant  of  impact  with  the 
earth  a  certain  velocity  due  to  the  attraction  of  the  earth's  gravity, 
and  the  impact  will  result  in  a  certain  degree  of  heat  on  account 
of  the  accelerated  movement  of  the  molecules  of  matter  due  to 
the  impact.  If  dropped  from  a  greater  height,  the  velocity  of 
the  falling  stone,  the  impact  and  the  heat  generated  thereby  will 
all  be  correspondingly  greater.  Science  has  determined,  to  its 
own  satisfaction  at  least,  the  limits  of  the  earth's  attraction  and 
maximum  speed  with  which  a  body  falling  through  space  from 
an  infinite  distance  would  approach  the  earth.  We  are  told 
that  the  utmost  limit  of  speed  with  which  our  planet  could  come 
into  contact  with  any  such  celestial  wayfarer,  in  head-on  collision, 
is  26  miles  per  second,  and  that  the  impact  resulting  from  such  a 
collision  would  result  in  the  generation  of  376,916  deg.  F.,  assum- 
ing that  the  total  quantity  of  heat  generated  by  the  impact  be 


HEAT  AND  COMBUSTION  5 

applied  to  a  mass  of  water  equal  in  weight  to  the  falling  body. 
Science  has  amused  itself  with  calculations  to  determine  the  heat 
generated  by  a  similar  collision  with  the  sun  and  other  bodies  of 
larger  diameter  than  the  earth.  It  would  be  idle  to  follow  the 
subject  further.  What  has  been  said  will  serve  in  a  way  as  in- 
troductory to  a  discussion  of  the  "  Mechanical  Equivalent  of 
Heat." 

THE  " MECHANICAL  EQUIVALENT  OF  HEAT" 

An  understanding  of  the  doctrine  of  the  "mechanical  equiva- 
lent of  heat "  is  of  great  importance.  The  laws  that  have  been 
formulated  in  connection  with  this  doctrine  underlie  the  science 
of  thermodynamics  and  have  a  direct  bearing  upon  all  branches 
of  steam  engineering. 

The  terms,  "  Force  "  and  "  Energy,"  have  been  employed  to  a 
great  extent  as  synonymous  by  physicists,  especially  in  Great  Brit- 
ain. The  tendency  of  late  has  been  to  limit  the  term,  "  Force," 
to  the  strict  Newtonian  definition,  viz.,  "Force  is  any  cause  which 
alters  or  tends  to  alter  a  body's  state  of  rest  or  of  uniform  motion 
in  a  straight  line."  "  Energy,"  in  the  broad  sense  of  the  term, 
"  is  the  capacity  for  performing  work  or  producing  a  physical 
change."  Energy  may  be  either  "  actual,"  as  for  instance  when 
a  weight  is  falling,  or  it  may  be  "potential"  as  when  a  weight  is 
suspended.  The  term,  "Energy  of  Position,"  is  employed  by 
some  writers  in  preference  to  "  Potential  Energy,"  while  other 
writers  combine  the  two  terms  and  speak  of  the  "  Potential  En- 
ergy of  Position."  A  swinging  pendulum  exhibits  both  forms  of 
energy.  When  in  motion  it  is  possessed  of  "actual"  energy. 
When  it  is  stationary  at  the  end  of  its  "swing"  and  before 
initiating  the  return  movement,  it  is  possessed  of  "potential 
energy"  or  "energy  of  position."  "Actual  energy"  is  based 
upon  and  arises  out  of  the  fact  of  "  potential  energy."  "  Force," 
accordingly,  is  a  display  of  "actual  energy"  and  "force"  may  in 
turn  give  rise  to  "  potential  energy." 

"Energy,"  in  the  broad  term,  is  a  constant  quantity,  —  like 
matter,  it  is  indestructible  and  cannot  be  created  or  destroyed. 
It  neither  increases  nor  diminishes  in  quantity.  If  it  were  sub- 
ject to  changes  in  quantity,  the  equilibrium  of  the  universe  would 
be  disturbed  and  chaos  would  reign  in  place  of  order.  While  the 
quantity  of  "energy"  remains  the  same,  it  may  manifest  itself  in 


6  COMBUSTION  AND  SMOKELESS   FURNACES 

a  multitude  of  forms.  We  have  it  in  the  form  of  gravitation,  in 
the  bolt  of  lightning,  in  the  shock  of  the  earthquake,  and  in  the 
expansion  of  steam  in  the  cylinder  of  the  engine.  Energy  may 
change  its  form  without  abating  in  any  degree  its  capacity  to  per- 
form work;  it  may  reappear  at  once  in  some  other  form,  or  it  may 
lie  dormant  for  ages,  ready  at  any  moment  to  reappear  upon  call 
in  all  its  vigor.  Take,  for  instance,  a  charge  of  gunpowder.  Here 
we  have  tremendous  energy,  inactive  and  dormant.  The  gun- 
powder is  exploded  in  a  cannon.  The  energy  is  immediately  re- 
leased and  almost  immediately  disappears.  What  has  become  of 
it?  A  portion  of  it  reappears  as  sound  waves,  a  portion  gives 
impetus  to  the  projectile,  and  other  portions  are  to  be  variously 
accounted  for.  What  becomes  of  the  force  imparted  to  the  pro- 
jectile? The  projectile  at  once  comes  into  contact  with  the 
atmosphere,  and  friction  accounts  for  a  portion.  It  comes  into 
impact  with  the  target  and  heat  energy  arises  and  gives  account 
for  a  portion.  Whence  comes  the  energy  in  the  coal?  It  was 
stored  there  as  dormant  heat  energy,  away  back  in  the  carbo- 
niferous period,  from  that  great  warehouse  of  light  and  heat,  the 
sun.  We  burn  the  coal  in  the  furnace  of  a  steam  boiler  and 
the  stored  heat  energy  at  once  responds.  We  cause  it  to  take 
the  form  of  mechanical  energy  and  once  again  it  disappears. 

Joule,  who  has  already  been  referred  to,  concerned  himself 
for  years  with  experiments  to  determine  the  "mechanical  equiva- 
lent of  heat";  in  other  words,  "what  amount  of  'mechanical 
energy'  is  equivalent  to  a  given  amount  of  'heat  energy'";  or 
in  other  words  again,  "if  a  given  amount  of  'mechanical  energy' 
is  caused  to  change  its  form  and  reappear  as  'heat  energy,'  what 
amount  of  'heat  energy'  will  be  produced?"  Water  is  employed 
very  largely  in  physical  experiments,  and  Joule  employed  it, 
referring  his  findings  to  water,  at  a  temperature  of  39  deg.  F., 
—  the  temperature  of  its  greatest  density.  He  took  the  amount 
of  heat  required  to  raise  one  pound  of  water  at  this  temperature, 
one  degree,  as  a  basis  for  his  computations.  Some  of  his  experi- 
ments were  quite  crude  and  simple.  For  instance,  he  caused  a 
paddle  to  be  mechanically  operated  in  a  basin  of  water.  He 
measured  the  mechanical  energy  employed,  and  also  the  tem- 
perature of  the  water.  He  finally  arrived,  by  a  process  of  ex- 
periments too  fine,  and  mathematical  operations  too  abstruse  to 
be  referred  to  here,  at  the  conclusion  that  the  amount  of  energy 


HEAT  AND  COMBUSTION  7 

displayed  as  heat  required  to  raise  the  temperature  of  one  pound 
of  water  one  degree  was  exactly  equivalent  to  the  amount  of 
energy  displayed  in  mechanical  form  required  to  raise  a  mass 
weighing  778  Ib.  a  distance  of  one  foot,  or  what  amounts  to  the 
same  thing  a  mass  weighing  one  pound  a  distance  of  778  ft. 
These  results  he  corrected  by  further  experiment  to  772.55. 
Joule  gave  to  the  world  of  science  the  British  thermal  unit.  A 
British  thermal  unit  or  1  B.  T.  U.  is  the  amount  of  heat  required 
to  raise  the  temperature  of  one  pound  of  water  at  39  deg.  F., 
one  degree.  One  B.  T.  U.  of  heat  transformed  into  "  mechan- 
ical energy  "  will,  according  to  the  Joule  determination,  raise  a 
mass  weighing  772.55  Ib.  one  foot.  Later  experimenters,  among 
them  Prof.  Rowland,  insist  that  the  original  finding  of  Joule,  — 
viz.,  778  foot  pounds  is  more  nearly  correct,  —  while  Reynolds 
and  others  give  us  figures  in  the  neighborhood  of  776.  Many  of 
the  highest  authorities  in  physics  and  many  of  the  leading  Amer- 
ican schools  have  adopted  the  Rowland  determination,  while 
others  adhere  to  the  final  figures  given  by  Joule.  The  Joule  unit 
is  generally  accepted  in  Great  Britain,  and  it  would  accordingly 
seem  consistent  to  follow  the  British  standard  or  cease  reckoning 
in  "  British  thermal  units  "  and  adopt  a  unit  of  our  own.  As  the 
Rowland  experiments  were  conducted  at  Baltimore,  it  would  be 
easy  for  those  who  prefer  the  Rowland  figure  to  substitute  "  Bal- 
timore "  for  "  British,"  and  thus,  while  not  abandoning  the  abbre- 
viation "  B.  T.  U. ",.  make  plain  what  they  mean  when  referring 
to  a  thermal  unit.  It  is  doubtful  if  an  international  standardizing 
of  the  thermal  unit  will  ever  be  effected,  for  the  reason  that  the 
foot  pound  varies  with  the  varying  force  of  gravitation,  —  the 
force  of  gravitation  in  any  locality  being  determined  by  the  density 
of  the  earth  in  that  region.  Gravity  is  measured  by  the  velocity 
of  bodies  falling  through  space.  In  ordinary  calculations  the 
velocity  increase  per  second  is  taken  in  the  United  States  at 
32.16  feet  and  in  England  at  32.2  feet. 

Now  that  the  thermal  unit  has  been  explained,  it  must  not 
be  lost  sight  of,  for  it  is  one  of  the  inheritances  of  steam  engineer- 
ing. It  enables  us  to  determine  many  things,  —  the  fuel  value 
of  coal  for  example.  Coal  has  value  as  a  fuel,  primarily,  only  in 
proportion  to  the  heat  units  it  contains.  When  the  coal  consumer 
discovers  that  he  is  at  the  mercy  of  the  coal  dealer  and 


8  COMBUSTION  AND  SMOKELESS   FURNACES 

awakes  to  a  full  realization  of  his  own  interests  he  will  buy  his 
fuel  by  heat  units  and  not  by  pounds.  The  consumer  is  inter- 
ested in  the  heat  unit,  and  the  price  of  it  when  he  contracts  for 
coal.  Other  considerations  are  of  but  secondary  importance. 
Self-interest  would  seem  to  suggest  some  method  of  checking 
up  on  the  deliveries  of  the  coal  dealer  to  determine  whether  he 
is  unloading  water,  dirt,  and  ash  in  place  of  heat  units,  and  whether 
the  actual  combustible  itself  is  calorifically  honest  or  dishonest. 

The  French  or  metric  heat  unit,  or  "calorie,"  is  the  amount 
of  heat  required  to  raise  one  kilogram  of  water  from  4  deg.  to 
5  deg.  C.  One  calorie  is  equivalent  to  3.968  British  thermal 
units. 

The  principle  that  "heat  energy  and  mechanical  energy  are 
mutually  convertible  "  has  its  limitations  in  mechanics.  If  it 
were  possible  to  transfer  one  unit  of  heat  energy,  without  loss, 
into  its  equivalent  in  mechanical  energy,  and  then  back  again  to 
one  unit  of  heat  energy,  and  repeat  the  operation,  we  should  have 
a  perfect  engine  and  the  problem  of  perpetual  motion  would 
be  solved. 

LATENT,   SENSIBLE    AND    SPECIFIC    HEAT 

Heat  possesses  a  number  of  peculiar  properties.  Its  dis- 
position to  disappear,  or  become  "latent,"  under  some  circum- 
stances, is  the  most  important  of  these  peculiarities,  both  from 
a  popular  standpoint  as  a  matter  of  interest  and  from  an  engi- 
neering standpoint  as  an  element  of  potentiality.  What  is  meant 
by  "sensible"  heat,  should  require  no  explanation.  The  ther- 
mometer registers  the  degree  of  "sensible"  heat.  "Latent" 
heat  is  not  "sensible"  to  our  bodies  or  to  the  fluid  in  the  ther- 
mometer. It  is  not  heat  at  all  in  the  popular  understanding  of 
the  term,  but  a  form  of  molecular  activity  which  is  able  to  sup- 
press from  the  senses  all  evidences  of  its  existence.  No  definition 
can  be  framed  that  will  understandingly  explain  "latent  heat." 
Resort  must  be  had  to  some  illustrations  of  the  way  in  which  it 
acts.  It  manifests  its  peculiarities  in  a  pronounced  way  in  the 
case  of  water. 

We  will  employ  a  piece  of  ice  for  our  experiments.  Now  if 
we  are  able  to  start  with  the  ice  at  the  "absolute  zero"  of  tem- 
perature, or  460.66  deg.  below  the  zero  of  the  Fahrenheit  scale 
and  add  heat  to  it,  the  heat  units  absorbed  will  manifest  their 


HEAT  AND  COMBUSTION  9 

presence  by  a  rise  in  the  temperature  of  the  ice.  This  rise  in 
temperature  will  be  substantially  uniform,  as  heat  is  added,  until 
we  reach  the  melting  point  of  ice,  —  32  deg.  F.  or  492.66  deg. 
absolute.  At  this  point  a  most  astonishing  thing  happens.  So 
long  as  a  vestige  of  the  ice  remains,  the  temperature  refuses  to 
rise  further.  We  may  add  heat  to  the  melting  ice  in  any  manner 
we  see  fit,  —  we  may  pour  boiling  water  upon  it  or  we  may  heat 
it  over  a  fire,  but  as  long  as  any  particle  of  the  ice  remains,  the 
thermometer  does  not  register  any  increase  in  temperature. 
Now  in  melting  a  pound  of  ice,  we  have  added  sufficient  heat  units 
to  have  raised  the  temperature,  had  the  heat  remained  "  sensible," 
283  deg.  or  to  315  deg.  F.  All  this  heat  is  slumbering  or  "  latent," 
ready  to  become  active  when  occasion  requires.  We  know  that 
this  is  so,  because  it  can  be  proved.  The  reader  may  have  proved 
it  himself,  without  knowing  it.  The  night  promises  to  be  cold 
and  you  are  afraid  the  plants  will  freeze.  You  place  a  tub  of 
water  in  the  room.  Why?  Because  you  have  been  told  the 
water  will  absorb  the  frost  and  save  the  plants.  Nothing  of  the 
kind  occurs.  When  ice  changes  to  water,  heat  is  absorbed  and 
becomes  dormant.  When  water  changes  to  ice,  this  dormant 
or  " latent"  heat  awakes  from  its  sleep  and  becomes  active  or 
"sensible."  It  warms  the  plants.  You  have  seen  open  water 
"steam"  on  a  cold  day.  It  is  giving  up  its  "latent  heat"  and 
going  back  to  ice.  It  is  usually  a  little  warmer  in  winter,  near 
large  bodies  of  water,  than  elsewhere  in  the  same  latitude.  We 
say  that  this  is  due  to  the  water.  The  water  has  nothing  to  do 
with  it  directly,  —  it  is  the  "latent  heat"  contained  in  the  water. 

But  let  us  get  back  to  the  pound  of  ice  that  we  have  melted 
to  water  at  a  temperature  of  32  deg.  We  add  more  heat  to  the 
water  and  the  temperature  begins  to  rise  again,  until  we  reach 
the  boiling  point  of  water,  —  212  deg.  F.  Add  as  much  more 
heat  as  we  please  to  it,  we  cannot  raise  the  temperature  the  frac- 
tion of  a  degree.  The  water  becomes  steam,  and  the  steam  has 
a  temperature  of  212  deg.  When  the  water  has  all  changed  to 
steam,  if  we  add  more  heat  the  temperature  of  the  steam  will 
rise.  Now  how  much  heat  became  "latent"  while  we  were 
changing  this  water  into  steam,  after  reaching  the  boiling  point? 
966.66  British  thermal  units,  —  enough  heat,  had  it  remained 
"sensible,"  to  have  raised  the  temperature  of  the  water  to  1178 
deg.  F.  Over  four  fifths  of  the  heat  that  we  have  added  to  the 

AUTHOR'S  NOTE:  Later  steam  tables  by  Marks  and  Davis, 
now  generally  adopted,  give  the  latent  heat  of  steam  a  value  of 
970.4  B.  T.  U. 


10  COMBUSTION  AND  SMOKELESS   FURNACES 

water  since  the  ice  was  completely  melted  has  become  " latent." 
In  this  "latent  heat  of  steam"  largely  resides  its  capacity  to  work 
for  us,  and  drive  the  wheels  of  our  mills  and  factories. 

When  the  steam  goes  back  to  water,  its  " latent"  heat  is  given 
up,  just  as  the  " latent"  heat  of  water  is  released  when  water 
goes  back  to  ice.  If  it  were  possible  to  convert  steam  to  water, 
without  losing  any  of  this  heat,  the  water  would  be  red  hot,  and 
if  we  could  convert  the  water  to  ice,  without  loss  of  heat,  the  ice 
would  be  white  hot. 

Heat,  in  its  " latent"  state,  causes  substances  to  change  their 
form.  It  causes  ice  to  change  to  water  and  water  to  change  to 
steam.  It  causes  gases  to  assume  a  more  rarified  state.  It  is 
thought  that  when  heat  manifests  itself  in  this  form  in  matter, 
the  molecules  are  given  a  disposition  to  repel  each  other,  and 
that,  as  a  consequence,  expansion  results.  Hence  we  have  the 
term,  "latent  heat  of  expansion,"  which  is  that  form  of  heat 
which  tends  to  an  increase  of  the  volume  of  the  substance  to 
which  it  is  applied. 

The  following  table  shows  the  proportions  of  "sensible"  and 
"latent"  heat,  in  British  thermal  units,  residing  in  one  pound 
of  saturated  steam  at  a  temperature  of  212  deg.;  also  the  "me- 
chanical equivalents"  in  foot  pounds: 


B.  T.  U. 

FOOT  POUNDS 

Sensible  Heat  

180.9 

139  655 

Latent  Heat  

966.66 

745,134 

Total 

1,147.56 

884,789 

It  is  interesting  to  note  just  how  these  two  forms  of  heat 
express  themselves  at  the  cylinder  of  the  engine.  The  bulk  of 
the  work,  to  the  point  of  "cut-off,"  is  performed  by  the  "latent" 
heat  of  the  steam  that  is  in  the  act  of  generation  from  water  into 
steam  upon  the  heating  surfaces  of  the  boiler.  This  newly  gen- 
erated steam  forces  what  has  preceded  it  into  and  through  the 
mains  to  the  cylinder  of  the  engine  and  against  the  piston.  After 
"cut-off,"  the  work  is  performed  by  the  "sensible"  heat  con- 
tained in  the  steam  imprisoned  in  the  cylinder  and  the  "latent" 
heat,  which  reappears  upon  condensation,  if  condensation  occurs, 
as  "sensible."  If  no  condensation  occurs  in  the  cylinder,  it 


HEAT    AND   COMBUSTIOX  11 

follows  that  the  966.66  heat  units  lying  dormant  in  each  pound 
of  steam  are  rejected  from  the  cylinder  and  lost,  unless  means 
are  provided  to  utilize  them  by  heating  feed  water,  buildings, 
etc.  It  is  probable  that  in  cities  where  manufacturing  is  carried 
on  to  any  extent,  enough  heat  is  wasted  in  this  manner  to  keep 
every  family  comfortable  throughout  the  entire  winter. 

When  we  speak  of  the  " specific  heat"  of  any  substance,  we 
mean  the  capacity  or  ability  of  that  substance  to  absorb  heat, 
as  compared  with  water.  In  order  to  measure  anything,  we 
must  have  a  standard,  and  in  this  case  the  quantity  of  heat  re- 
quired to  raise  the  temperature  of  one  pound  of  water  one  degree 
Fahrenheit  is  taken  as  such  standard  of  measurement.  We 
accordingly  say  that  the  "specific  heat"  of  water  at  32  deg.  F. 
is  unity,  or  1,  and  that  the  " specific  heat"  of  air,  under  constant 
pressure,  is  0.2377  and  of  hydrogen  2.4096. 


CHAPTER  II 

COMBUSTION  AND  THE  BOILER  FURNACE 

WE  have  now  laid  sufficient  foundation,  by  our  investigation 
of  the  nature  and  properties  of  heat,  to  enable  us  to  proceed 
intelligently  with  a  discussion  of  combustion.  "  Combustion," 
as  we  denned  it  in  the  outset,  is  "the  chemical  union  of  com- 
bustible matter  with  oxygen,  'the  supporter  of  combustion.'" 
As  a  result  of  such  union  the  molecules  of  matter  are  forced  to 
adjust  themselves  in  new  relations,  —  motion  and  friction  occur 
and  heat  is  developed. 

Combustion  may  be  slow  and  accompanied  by  little  heat,  as 
when  iron  rusts;  it  may  be  more  rapid,  as  when  it  occurs  in  the 
lungs  of  animals  and  what  we  call  "animal  heat"  is  developed; 
it  may  be  still  more  violent,  as  when  coal  is  burned  in  a  furnace, 
or  it  may  be  instantaneous,  as  when  powder  is  exploded  in  a  gun 
barrel.  The  speed  of  combustion  depends  primarily  upon  the 
chemical  affinity  of  the  elements  of  the  combustible,  for  oxygen, 
and  secondarily  upon  the  conditions  under  which  the  combustion 
takes  place.  Hence,  when  we  are  seeking  a  combustible  for 
commercial  purposes,  we  must  select  something  having  a  ready 
affinity  for  oxygen,  and  we  find  that  carbon  and  hydrogen  meet 
the  requirements.  We  have  these  two  elements  combined  in 
coal,  the  carbon  largely  predominating.  Nature  has  furnished 
us  with  these  combustibles,  and  also  with  the  supporter  of  com- 
bustion, but  man  is  compelled  to  supply  the  necessary  conditions 
to  render  chemical  union  possible  at  a  rate  sufficiently  rapid  to 
serve  his  purposes.  Chief  of  these  conditions  of  rapid  combus- 
tion is  temperature.  "Heat  aids  all  chemical  action."  When 
a  sufficient  "nest  egg"  of  temperature  is  furnished,  combustion 
is  instituted  and  thereafter,  itself,  furnishes  the  temperature 
necessary  to  its  continuance.  The  burning,  or  combustion,  of 
any  fuel,  coal  for  instance,  accordingly  contemplates  two  opera- 
tions. The  first  operation  is  a  physical  one,  and  consists  of 

12 


COMBUSTION  AND  THE  BOILER  FURNACE 


13 


raising  the  temperature  of  the  fuel  by  artificial  means  to  a  point 
where  the  second  operation,  that  of  chemical  combination,  may 
ensue.  In  other  words,  we  must  first  light  the  fire.  Our  famil- 
iarity with  this  operation  must  not  lead  us  to  think  that  it  in- 
volves matters  of  no  more  interest  than  matches  and  kindling. 
The  commonness  of  any  phenomenon  must  not  be  taken  as 
evidence  of  its  unimportance.  In  this  instance,  the  question 
of  temperatures  as  related  to  ignition  is  one  of  the  most  impor- 
tant in  the  whole  range  of  our  discussion  of  combustion  as  con- 
cerned with  steam  boiler  furnaces.  The  various  aspects  of  the 
subject  will  be  touched  upon  in  their  proper  order. 

So  much  in  a  general  way  as  to  combustion;  let  us  now  note 
more  particularly  what  takes-  place  in  the  furnace  of  a  steam 


i 


n 


FIG.  1 

boiler  when  bituminous  coal  is  burned.  We  will  assume  the 
case  of  an  ordinary  return  flue,  multitubular  boiler,  mounted 
and  set  in  the  usual  way,  with  an  ordinary  grate  and  fire-box, 
having  a  bridge  wall  at  the  rear.  Reference  may  be  had  to  the 
accompanying  drawing,  Fig.  1.  We  will  assume  the  fire  lighted 
and  the  boiler  in  ordinary  service  operation.  We  will  start  our 
observations  with  a  " coked"  fire.  The  volatile  elements  have 
all  been  distilled  from  the  coal  and  the  stack  is  clear  of  what  is 
commonly  called  "  smoke."  The  fuel  is  burning  slowly,  with 
an  incandescent  glow,  and  the  boiler  is  receiving  heat  by  convec- 
tion from  the  escaping  gases  of  combustion,  and  by  radiation 
from  the  incandescent  fuel.  There  is  no  flame  at  any  point  in 
contact  with  the  boiler  shell.  What  is  the  nature  of  the  chem- 


14  COMBUSTION   AND  SMOKELESS   FURNACES 

ical  reactions  that  are  taking  place  while  the  fire  is  in  this  con- 
dition? Air  is  entering  at  the  ash-pit  doors,  and  is  being 
"drawn"  up  through  the  grates  and  fuel  by  the  chimney  draft. 
We  use  the  word  " drawn"  because  it  is  implied  by  the  term 
"draft."  Now  draft,  as  it  occurs  in  a  chimney,  is  not,  strictly 
speaking,  a  pull,  but  may  be  more  accurately  defined  as  a 
"push."  Draft  is  due,  as  everybody  ought  to  know,  to  the 
difference  in  weight  between  the  column  of  air  that  has  its 
base  at  the  bottom  of  the  inside  of  the  chimney,  and  a  column 
of  air  of  equal  dimensions  that  has  its  base  outside  the  chim- 
ney. Now  the  air  and  gases  within  the  chimney  contain  a 
certain  amount  of  "latent"  heat,  —  the  "latent  heat  of  expan- 
sion"—  and,  owing  to  the  fact  that  they  are  expanded,  weigh 
less  per  cubic  foot  than  the  corresponding  air  in  the  other  column. 
A  struggle  for  equilibrium  takes  place,  and  in  this  struggle  the 
lighter  column  is  displaced  or  "pushed  out"  by  the  heavier  one. 
It  would  avoid  many  misconceptions  if  engineering  language 
were  more  accurate  in  its  terminology. 

Air  is  composed  chiefly  of  nitrogen  and  oxygen,  about  21  per 
cent,  by  volume  and  23  per  cent,  by  weight  being  oxygen.  With 
the  nitrogen  we  have  no  concern,  for  there  is  no  practical  way 
of  eliminating  it.  It  serves  no  office  in  combustion,  and  is  a 
dead  weight  upon  the  furnace,  boiler,  and  chimney,  requiring 
space  for  its  accommodation  and  absorbing  and  carrying  off  heat 
units  that  might  otherwise  be  employed  in  the  manufacture  of 
steam.  The  oxygen  we  must  have,  and  it  is  cheaper  to  make 
the  best  of  the  undesired  company  of  nitrogen,  than  to  attempt 
divorcement  of  the  elements.  Oxygen  has  a  strong  affinity  for 
carbon,  and  it  finds  its  carbon  upon  the  grate,  heated  to  a  con- 
dition making  rapid  chemical  union  possible.  The  oxygen 
separates  itself  from  mechanical  union  with  the  nitrogen,  and 
unites  in  chemical  union  with  the  carbon  in  the  proportion  of 
one  atom  of  carbon  to  two  of  oxygen.  The  chemical  compound 
resulting  is  known  as  carbonic  acid  gas  or  carbon  dioxide,  repre- 
sented by  the  chemical  symbol  (C02),  which  not  only  stands  for 
the  compound  but  the  proportions  of  the  elements  entering  into 
it.  This  reaction  or  combination  occurs  as  soon  as  the  oxygen 
and  carbon  get  into  contact  with  each  other,  in  the  lower  strata 
of  fuel.  When  one  atom  of  carbon  unites  with  two  of  oxygen, 
the  atom  of  carbon  is  completely  oxidized  or  satisfied  with  oxygen. 


COMBUSTION   AND  THE   BOILER  FURNACE  15 

The  oxygen,  however,  is  not  satisfied  with  carbon,  or  is  not  com- 
pletely "carbonized,"  if  we  may  use  the  term  in  this  connection. 
The  compound  (CO2)  which  represents  complete  combustion  or 
oxidization  of  the  combustible  carbon,  now  takes  its  way,  under 
the  influence  of  the  draft,  up  through  the  incandescent  bed  of 
fuel  and  emerges  into  the  fire-box  of  the  furnace.  But  it  has 
undergone  a  change  in  transit.  The  carbon  of  the  compound 
(CO2)  was  fully  satisfied  with  oxygen,  but  the  oxygen  was  hungry 
for  more  carbon  and,  meeting  with  carbon  in  the  passage  through 
the  upper  strata  of  the  fuel,  picked  up  another  atom  of  that  ele- 
ment. The  gas  that  emerges  into  the  fire-box  is  accordingly  ex- 
plained by  the  reaction  C02  +  C  =  2(CO).  It  contains  equal 
parts  of  carbon  and  oxygen,  and  is  known  as  carbon  monoxide. 
The  oxygen  of  this  compound  is  fully  satisfied  with  carbon,  or 
"  carbonized, "  as  we  have  taken  the  liberty  of  expressing  it,  but 
the  carbon  of  the  compound  is  not  fully  oxidized  and  is  hungry 
for  oxygen.  The  gas  is  accordingly  combustible  in  its  new  state, 
as  it  is  capable  of  further  oxidization.  Free  oxygen  is  required, 
and  if  we  are  to  burn  this  gas,  air  must  in  some  manner  be  ad- 
mitted into  the  fire-box.  Carbon  monoxide,  as  it  arises  from 
coke,  is  a  colorless  and  odorless  gas.  It  does  not  manifest  its 
presence  at  the  top  of  the  chimney  in  visible  smoke  at  this  time, 
and  we  must  here  make  the  observation  that  a  clear  stack  is  not 
necessarily  evidence  of  complete  combustion.  A  considerable 
quantity  of  carbon  monoxide,  or  coke  gas,  may  be  escaping  un- 
burned.  A  "coked'*  fire  accordingly  requires  a  certain  amount 
of  free  oxygen  in  the  fire-box  for  the  accommodation  of  this  gas, 
although  the  amount  demanded  is  inconsiderable  as  compared 
with  the  requirements  during  the  time  that  the  coal  is  in  process 
of  "coking,"  as  will  be  shown.  Carbon  monoxide  burns  with  a 
purple  flame,  and  if  such  a  flame  is  present  on  the  surface  of  the 
coked  fuel,  it  is  evidence  that  the  gas  is  being  consumed.  If  this 
flame  is  absent,  the  supply  of  air  entering  the  fire-box  should  be 
slightly  increased,  either  through  the  dampers  in  the  fire  doors 
or  otherwise,  but  great  care  should  be  exercised  to  make  certain 
that  we  are  not  admitting  air  in  excess  of  the  requirements,  as 
in  such  case  the  surplus  air  will  cause  a  loss  to  exceed  the  gain 
that  we  are  making  by  burning  the  carbon  monoxide. 

A  fact  of  supreme  importance  requires  consideration  at  this 


16  COMBUSTION  AND  SMOKELESS   FURNACES 

juncture.  It  is  fully  set  out  in  what  is  known  as  "Bertholet's 
Second  Law."  Bertholet  was  a  celebrated  French  chemist  who 
flourished  in  the  early  part  of  the  last  century,  and  his  Second 
Law  is  as  follows: 

"  The  heat  produced  in  a  furnace  depends  on  the  final  product 
of  combustion  and  not  at  all  on  whether  the  carbon,  for  example, 
has  been,  at  intermediate  stages,  wholly  or  partly  burned,  and 
has  existed  in  a  greater  or  less  proportion  in  the  state  of  carbon 
monoxide  or  dioxide." 

In  other  words,  the  final  results  are  determined  by  the  final 
conditions.  The  quantity  of  heat  given  to  the  boiler  is  deter- 
mined by  the  final  state  of  the  gas  escaping.  In  tracing  the 
reactions  that  take  place  when  oxygen  has  access  to  incandescent 
coke,  we  discovered  that  the  first  chemical  combination  occurring 
after  the  oxygen  passed  the  grates  resulted  in  the  formation  of 
(CO2).  The  carbon  entering  into  this  compound  becomes  com- 
pletely oxidized,  and  in  this  process  yields  all  the  heat  energy  it 
contains.  If  this  gas  could  have  access  to  the  boiler  shell,  the 
maximum  of  the  heat  contained  in  the  carbon  could  be  employed 
in  the  manufacture  of  steam.  But  we  also  discovered  that  this 
gas,  before  it  has  an  opportunity  to  reach  the  heating  plates  of 
the  boiler,  is  converted  to  (CO),  and  in  this  conversion  or  " reac- 
tive reduction,"  heat  is  absorbed  and  disappears.  Hence  the 
heat  of  the  gas  emerging  from  the  fuel  bed  and  approaching  the 
boiler  shell  is  the  heat  of  (CO)  and  not  of  (CO2).  Every  process 
tending  toward  oxidization  releases  heat;  every  process  tending 
away  from  oxidization  absorbs  heat.  The  following  table  will 
show  how  important  it  is  that  the  gas,  carbon  monoxide,  should 
be  converted  to  carbon  dioxide  before  reaching  the  shell  of  the 
boiler: 

One  pound  of  Carbon  burned  to  Carbon  Dioxide,  (CO2), 

yields  in  British  Thermal  Units 14,540 

One  pound  of  Carbon,  burned  to  Carbon  Monoxide,  (CO), 

yields  in  British  Thermal  Units 4,350 

Loss  in  Heat  Units 10,190 

It  is  of  course  probable  that  some  free  air  would  find  its  way 
through  crevices  in  the  fuel  bed,  and  that  in  actual  practice  the 
loss  would  be  much  less  than  indicated  by  the  table,  even  assum- 
ing the  entire  suppression  of  air  introduction  by  way  of  the  fire 


COMBUSTION   AND  THE   BOILER   FURNACE  17 

doors,  by  percolation  through  the  walls  of  the  boiler  setting,  or 
otherwise.  The  table  is,  however,  very  instructive  as  indicating 
the  possibilities  of  loss  contained  in  the  situation. 

It  does  not  follow,  however,  that  we  can  secure  complete 
combustion  of  the  "coke  gas"  we  have  been  considering,  or  the 
"coal  gas"  we  are  about  to  consider,  by  the  mere  expedient  of 
introducing  oxygen.  An  igniting  temperature  must  be  provided, 
and  this  temperature  must  exist  in  the  presence  of  the  oxygen, 
otherwise  we  shall  have  no  combustion.  The  builders  of  steam 
boilers  have  neglected  in  most  cases  to  make  the  necessary  pro- 
visions for  the  maintenance  of  such  temperature.  Their  atten- 
tion has  been  focused  upon  the  problem  of  "heat  absorption" 
to  such  an  extent  that  they  have  overlooked  many  matters  in- 
volved in  the  question  of  combustion.  Let  us  see  how  the  ordi- 
nary return  tubular  boiler  and  the  common  form  of  setting,  as 
shown  in  Fig.  1,  interpose,  agencies  tending  to  retard  combustion 
rather  than  contribute  to  its  complete  fulfilment. 

At  the  rear  of  the  grates  is  a  barrier,  commonly  known  as  a 
"bridge  wall."  In  addition  to  serving  as  a  wall  for  the  rear  of 
the  furnace  and  preventing  the  escape  of  fuel  into  the  combustion 
chamber  at  the  rear,  the  " bridge  wall"  tends  to  direct  the  cur- 
rents of  flame  and  heated  gases  against  the  boiler  shell.  The 
boiler  builder  aims  to  get  these  currents  in  contact  with  the  heat- 
ing plates  as  soon  as  possible,  in  order  that  they  may  be  in  con- 
tact as  long  as  possible,  and  thus  convey  to  the  water  within  the 
boiler  the  maximum  amount  of  heat  permitted  by  the  conduc- 
tivity of  the  boiler  plates.  His  efforts  in  this  direction  tend  to 
check  and  retard  the  combustion  of  the  escaping  gases.  The 
boiler  shell  is  cold,  relatively  speaking.  Its  temperature  is  sub- 
stantially that  of  the  contents  of  the  boiler.  Water  boils  under 
atmospheric  pressure  at  a  temperature  of  212  deg.  F.  Under  a 
steam  pressure  of  100  Ib.  it  boils  at  a  temperature  of  337.9  deg.  It 
is  safe  to  say  that  the  shell  of  the  average  boiler  will  not  be  hotter 
than  about  400  deg.,  while  the  temperature  of  the  fire  immediately 
under  it  may  be  as  high  as  3000  deg.  The  gases  in  such  a  case  are 
subjected  to  the  tremendous  drop  of  2600  deg.  in  extraneous 
temperatures,  in  passing  from  the  fuel  bed  to  the  boiler  shell. 
We  can  more  fully  appreciate  these  figures  when  we  stop  to  con- 
sider that  the  drop  from  the  boiling  point  to  ice  water  is  only 
180  deg.  Combustion  depends  as  much  upon  the  maintenance 


18  COMBUSTION  AND  SMOKELESS   FURNACES 

of  the  igniting  temperature  as  it  does  upon  the  agency  of  oxygen. 
Can  any  one,  after  studying  Fig.  1  in  the  light  of. these  facts, 
express  wonder  that  the  stack  of  the  ordinary  boiler  emits  smoke, 
which  is  always  a  prima  facie  evidence  of  incomplete  combustion? 
These  chilling  influences  may  be  neutralized  to  some  extent  by 
lowering  the  grates  and  thereby  increasing  the  distance  between 
fuel  bed  and  boiler.  Combustion  should  be  given  all  the  oppor- 
tunities possible  to  complete  its  operations  before  the  gases  are 
subjected  to  the  possibilities  of  refrigeration  contained  in  the 
cold  boiler  shell. 

A  few  simple  experiments  will  serve  to  verify  the  truth  of  the 
foregoing  statements  with  reference  to  temperature  and  the  effect 
of  a  chilling  surface  upon  the  combustion  of  a  gaseous  fuel.  Place 
a  dish,  or  anything  presenting  a  cold  surface,  in  the  flame  of  an 
ordinary  gas  jet.  Carbon  is  at  once  precipitated  in  a  fine  powder, 
and  black  smoke  is  formed.  The  extent  of  such  precipitation 
registers  the  degree  in  which  combustion  has  been  checked. 
When  the  ordinary  kerosene  lamp  is  first  lighted,  it  is  likely  to 
smoke  for  a  few  moments,  if  turned  up  to  its  full  capacity.  This 
is  due  to  the  fact  that  the  chimney  and  the  air  within  the  chimney 
are  cold,  or  at  least  not  hot  enough  to  insure  such  a  state  of  com- 
bustion as  is  necessary  to  smokelessness.  The  lamp  will  also 
serve  to  illustrate  the  office  of  oxygen  in  combustion.  Place  a 
card  near  the  top  of  the  chimney.  This  will  obstruct  the  draft 
passing  up  through  the  chimney,  and  the  lamp  will  smoke.  If 
the  screen  upon  which  the  chimney  rests,  and  which  admits  air 
to  the  flame,  becomes  filled  with  dirt,  or  the  flow  of  air  is  inter- 
rupted in  any  other  manner,  the  lamp  will  smoke. 

Air  and  temperature  are  accordingly  both  necessary  to  the 
complete  combustion  of  the  gases  arising  from  soft  coal.  If 
either  is  lacking,  there  will  be  smoke.  The  temperature  of  the 
fire-box  may  be  raised  to  any  degree  required,  but  if  the  supply 
of  oxygen  is  deficient,  there  will  be  smoke.  Coal  may  be  burned 
in  the  open  air  where  the  supply  of  oxygen  is  absolutely  unlimited, 
and  there  will  be  smoke.  The  necessary  temperature  does  not 
exist,  —  heat  is  dissipated  as  fast  as  generated. 

We  will  now  suppose  that  the  furnace  of  the  boiler  under 
consideration,  and  illustrated  in  Fig.  1 ,  is  stoked  with  fresh  coal. 
We  will  follow  the  physical  and  chemical  operations  that  ensue 
and  see  what  takes  place. 


COMBUSTION   AND  THE   BOILER   FURNACE 


19 


The  fuel  elements  contained  in  coal  are  of  two  classes,  — 
fixed  and  volatile.  The  proportions  that  these  elements  bear 
to  each  other,  of  course,  vary  widely  in  different  coals.  The 
following  table  approximately  expresses  the  composition  of  the 
several  classes  of  coal: 


FIXED  CARBON 
PER  CENT.  OF 
COMBUSTIBLE 

VOLATILE  MATTER 
PER  CENT.  OF 
COMBUSTIBLE 

Anthracite  

100  to  92 

0  to    8 

Semi-Anthracite  

92  to  87 

8  to  13 

Semi-Bituminous 

87  to  75 

13  to  25 

Bituminous 

75  to  50 

25  to  50 

Lignite  .                                              .    . 

Below  50 

Over  50 

We  will  assume  that  bituminous  coal  is  being  employed  in 
the  case  of  the  boiler  under  consideration,  and  that  the  vola- 
tile matter  is  37J  per  cent,  of  the  combustible,  which  would  be 
about  the  average  for  bituminous  coal,  according  to  the  above 
table. 

As  our  observations  have  up  to  this  time  been  limited  to  the 
fixed  carbon  or  coke  element  of  the  coal,  and  the  gases  that  result 
from  its  combustion,  and  as  we  are  now  about  to  observe  the 
combustion  of  the  volatile  elements,  which  are  so  widely  different 
in  nature  from  the  fixed  carbon,  we  will  do  well  to  make  some 
preliminary  inquiries  before  commencing  observation. 

The  gases  we  are  now  about  to  encounter  we  will  term  "coal 
gases,"  to  distinguish  them  from  the  "coke  gases"  already  in- 
vestigated. We  shall  find  that  carbon  and  hydrogen  enter  very 
largely  into  their  composition,  which  justifies  the  use  of  the  terms 
"hydrocarbon"  and  "carburetted  hydrogen."  If  we  submit 
the  volatile  matter  to  the  laboratory,  we  shall  be  amazed  at  the 
multiplicity  and  complexity  of  the  derivable  products.  Some 
of  these  are  as  follows : 

I.    ILLUMINATING  GASES 

SYMBOL  SYMBOL 

Acetylene (C2H2)      Ethylene (C2H4) 

Propylene (C3HB)      Butylene • (C<H«) 


Benzol  . 


II.     VAPORS 
(C6H«)      Naphthalin 


20  COMBUSTION  AND  SMOKELESS   FURNACES 

III.    DILUENTS  AND  "IMPURITIES" 

Hydrogen (H)  Light  Carburetted  Hydrogen . .  (CH4) 

Carbon  Monoxide (CO)  Carbon  Dioxide (CO2) 

Ammonia (NH3)  Cyanogen (C2N2) 

Bisulphide  of  Carbon (CS2)  Sulphuretted  Hydrogen (H2S) 

Oxygen (O)  Nitrogen (N) 

Water  vapor (H2O) 

IV.    COAL  TAR  COMPONENTS 

Toluol (C7H8)  Cumol (C9H12) 

Anthracene (C14H10)  Pyrene (Ci6Hi0) 

Crysone (C,8H12)  Carbolic  Acid (C6H6O) 

Cresylic  Acid (C7H8O)  Rosolic  Acid (C20Hi6O3) 

Pyridine (C5H5N)  Analine (C6H5NH2) 

Picoline (C6H7N)  Lutidine (C7H9N) 

Collidine (C8HUN)  Leucoline (C9H7N) 

V.    AMMONIACAL  LIQUORS 

Ammonium  Carbonate (NH4CO3)      Ammonium  Sulphydrate. .  .(NH4HS) 

Ammonium  Sulphpcyanate(NH4NCS)      Ammonium  Cyanide (NH4NC) 

Ammonium  Chloride (NH4C1) 

Here  we  have  many  of  the  commercial  drugs,  dyes,  acids,  and 
alkalis,  etc.,  that  find  a  sale  over  the  counters  of  the  drug  store. 
It  seems  like  sinful  prodigality  to  consign  them  to  the  furnace  of 
the  steam  boiler.  The  time  may  come,  and  some  engineers 
already  see  it  in  sight,  when  the  volatile  elements  of  coal  will  be 
distilled  on  a  large  scale  for  the  sake  of  the  by-products,  which 
will  enable  coke  to  be  placed  upon  the  market  at  a  price  suffi- 
ciently low  to  justify  its  general  use  in  large  centers  where  the 
smoke  nuisance  is  a  menace  to  public  health. 

The  fireman  places  a  quantity  of  green  coal  in  the  furnace 
upon  the  incandescent  coke.  One  of  the  first  effects  to  be  noted, 
if  we  are  equipped  with  sufficiently  sensitive  pyrometers,  is  a 
marked  lowering  of  the  temperature  of  the  fire-box.  The  heat  of 
the  coked  fuel  is  being  transformed  into  energy,  and  the  energy 
is  being  employed  in  the  distillation  of  the  volatile  elements  of 
the  coal.  The  green  coal  is  adding  nothing  to  the  heat  of  the 
furnace,  —  on  the  contrary  it  is  absorbing  heat  and  lowering  the 
temperature.  Distillation  of  the  volatile  matter  must  precede 
its  combustion,  and  takes  place  at  a  temperature  much  lower 
than  that  necessary  to  combustion.  We  will  note  that  as  distil- 
lation proceeds,  the  lumps  of  coal  swell  and  soften  under  the 
influence  of  the  heat,  and  that  when  distillation  is  completed 
these  lumps  of  coal  are  transformed  into  lumps  of  coke,  much 


COMBUSTION    AND    THE    BOILER    FURNACE  21 

lighter  than  the  original  coal  and  more  or  less  porous.  We  also 
note  that  the  first  vapors  to  rise  from  the  coal  are  light  in  color. 
These  vapors  consist  largely  of  steam.  The  moisture  contained 
in  the  coal  is  being  driven  off.  The  vapors  shade  from  light  to 
gray,  then  to  brown,  and  finally  to  a  darker  hue.  The  more 
volatile  of  the  elements  are  first  driven  off,  followed  by  the  heavier 
ones.  It  must  not  be  understood  that  each  one  of  the  volatile 
elements  named  in  the  above  tables  is  isolated  in  the  furnace  of 
the  boiler.  The  elements  are  most  likely  given  off  in  mixtures, 
according  to  their  natures  and  affinities.  There  will  probably 
be  light  compounds  of  carburetted  hydrogen,  known  as  "  marsh 
gas,"  heavier  compounds  of  carburetted  hydrogen,  known  as 
"olefiant"  or  oil-producing  gas,  and  certain  sulphur  and  ammonia 
compounds.  If  we  should  distill  these  gases  in  a  laboratory  at  a 
uniform  low  red  heat,  we  might  isolate  a  large  proportion  of  the 
compounds.  The  extent  of  the  isolation  would  depend  largely 
upon  the  temperature  and  other  circumstances  accompanying  the 
distillation.  If  the  coal,  for  instance,  is  coked  in  a  retort  at  a  gas 
works,  a  low  temperature  will  be  employed  and  the  products  will 
be  few  in  number.  The  results  from  a  ton  of  coal  coked  in  this 
manner  will  be  somewhere  within  the  following  figures,  depend- 
ing upon  the  nature  and  composition  of  the  coal : 

Pounds  of  coke 700  to    1,500 

Cubic  feet  of  gas 9,000  to  15,000 

Pounds  of  coal  tar 100  to       700 

Pounds  ammonia  liquor 60  to       160 

The  hydrocarbons  contained  in  coal  are  closely  related  in 
nature  and  composition  to  other  well  known  hydrocarbon  oils 
and  gases,  and  are 'of  great  fuel  value  due  to  the  presence  of  hy- 
drogen. One  pound  of  hydrogen  will  usually  be  found  in  bitu- 
minous coal  for  every  seventeen  pounds  of  carbon.  As  the  carbon 
is  found  in  two  forms,  fixed  and  volatile,  and  the  hydrogen  is 
found  in  compound  with  the  volatile  form  only,  it  will  be  under- 
stood why  a  pound  of  volatile  hydrocarbon  fuel  contains  more 
heat  units  than  an  equal  weight  of  fixed  carbon.  The  following 
table  shows  the  value  in  heat  units  of  a  pound  of  carbon  and 
equal  weights  of  hydrogen,  some  of  the  hydrocarbon  compounds, 
and  the  oxides  of  carbon.  The  table  also  contains  other  interest- 
ing data  of  value  at  this  stage  of  our  investigations: 


22 


COMBUSTION  AND  SMOKELESS   FURNACES 


COMBUSTIBLE 

B.  T.  U. 
PER  POUND 

POUNDS  AIR 
REQUIRED  PER 
POUND   COMBUSTIBLE 

POUNDS   WATER 
EVAPORATED   FROM 
AND  AT  212° 

Carbon  

14,540 

12. 

14  67 

Carbon  Monoxide 

10,100 

6 

10  4 

Hydrogen  
Olefiant  Gas  

62,032 
21,344 

36. 
1543 

62.6 
22  1 

Marsh  Gas  

26,400 

16.2 

26.68 

It  appears  from  the  table  that  the  heat  value  increases  in 
proportion  to  the  increase  of  hydrogen.  We  now  return  to  our 
observations  of  the  burning  fuel  in  the  boiler  furnace,  with  an 
increased  respect  for  the  volatile  part  of  it,  as  we  have  learned 
that,  pound  for  pound,  the  hydrocarbons  contain  more  heat  units 
and  are  consequently  of  greater  fuel  and  commercial  value  than 
the  fixed  carbon. 

We  note  that  as  the  temperature  of  the  furnace  rises,  little 
tongues  of  flame  leap  along  the  rising  gas  clouds  and  that  the 
flame  steadily  increases  in  volume  as  the  temperature  rises.  The 
character  of  the  flame  also  changes.  In  its  early  stages  it  is 
streaked  with  red  and  tipped  with  streamers  of  brown  and  black 
smoke.  If  the  temperature  continues  to  rise,  and  we  admit  a 
little  air  by  way  of  the  doors  or  otherwise,  we  will  note  an  in- 
crease in  the  length  of  the  flame,  a  decrease  in  the  length  of  the 
smoke  streamers,  and  that  the  flame  changes  from  a  reddish  cast 
to  a  bright  yellow.  If  we  look  at  the  stack  we  will  observe  less 
volume  of  smoke  than  was  present  when  the  flame  presented  a 
reddish  appearance.  If  the  temperature  rises  to  a  sufficient 
height,  and  we  admit  still  more  air,  we  shall  find  that  there  is 
another  change  in  the  character  and  appearance  of  the  flame. 
It  is  now  much  shorter  than  formerly,  and  is  white  to  the  point 
of  incandescence.  The  smoke,  when  we  observe  the  stack,  has 
greatly  diminished  if  it  has  not  entirely  disappeared.  The  chances 
are  that  we  shall  still  see  more  or  less  smoke,  as  the  cold  boiler 
shell,  when  the  burning  gases  reach  it,  will  check  and  perhaps 
entirely  halt  the  processes  of  combustion,  and  unconsumed  or 
unoxidized  carbon  will  be  precipitated  and  give  color  to  the 
escaping  gases.  If  we  are  by  any  means  able  to  maintain  the 
requisite  temperature,  and  introduce  the  necessary  amount  of 
oxygen,  the  smoke  will  entirely  disappear,  —  we  shall  be  getting 
complete  combustion. 


COMBUSTION    AND   THE    BOILER    FURNACE  23 

Our  observation  of  the  flame  in  the  fire-box  leads  us  to  ask 
several  questions  concerning  it.  What  is  flame?  It  is  combus- 
tible matter  in  process  of  being  oxidized.  What  causes  it  to  be 
luminous?  The  luminosity  is  due  to  the  heating  to  incandescence 
of  the  unconsumed  particles  of  matter  floating  in  the  gas  currents. 
The  variation  in  the  colors  of  the  flame  is  due  to  differences  in 
the  degree  of  heat  communicated  to  these  floating  particles  of 
combustible  matter.  The  higher  these  particles  are  heated,  the 
whiter  the  flame.  The  decrease  in  the  length  and  volume  of  the 
flame  is  due  to  a  decrease  in  the  number  of  the  floating  particles. 
The  number  decreases  in  proportion  to  the  completeness  or 
thoroughness  of  combustion.  When  the  molecule  of  carbon  is 
completely  oxidized,  it  loses  its  identity  in  the  compound  into 
which  it  enters.  The  particles  of  matter  take  on  a  form  of  such 
tenuity  that  incandescence  disappears,  notwithstanding  the 
continued  presence  of  the  heat.  The  appearance  of  the  flame  in 
the  furnace  accordingly  enables  us  to  determine  a  number  of 
things.  It  tells  us  of  the  extent  or  degree  of  combustion.  The 
whiter  and  shorter  the  flame,  the  better  the  combustion.  It 
tells  us  also  of  the  temperature  of  the  furnace.  The  following 
table  will  be  useful  in  this  connection: 


APPEARANCE  OF  FUEL  OR  FLAME 

TEMPERATURE 
FAHR. 

Dark  Red.. 

977° 

Dull  Red  
Dull  Cherry  Red  -.  

1290° 
1470° 

Full  Cherry  Red  

1650° 

Clear  Cherry  Red                                                                     .    . 

1830° 

Deep  Orange                                                                     

2010° 

White  

2370° 

Bright  White  

2550° 

Dazzling  White  

2730° 

It  is  not  necessary  to  observe  that  a  high  temperature  ac- 
companies complete  combustion,  and  that  the  performance  of 
the  boiler  as  to  efficiency  will  have  a  direct  relation  to  the  tem- 
perature and  consequently  to  the  completeness  of  combustion. 

We  have  much  more  accurate  means  of  determining  the  degree 
of  combustion  than  is  afforded  by  an  inspection  of  the  flame  in 
the  furnace.  We  may  determine  the  character  of  the  escaping 
flue  gases,  and  the  percentage  of  the  gases  that  indicate  complete 


24  COMBUSTION  AND  SMOKELESS   FURNACES 

combustion  of  the  carbon.  We  are  forced  in  such  flue  gas  anal- 
ysis to  disregard  the  hydrogen,  as  the  product  resulting  from  the 
combustion  or  oxidization  of  hydrogen  is  water,  (H20).  The 
coal  will  contain  moisture  to  some  extent  and  the  air  may  be 
more  or  less  moisture  laden.  It  follows  that  the  presence  of 
water  vapor,  or  steam,  in  the  stack  gases  might  have  no  connec- 
tion whatever  with  the  combustion  of  hydrogen  or  hydrocarbon 
volatile  matter.  With  carbon,  however,  it  is  a  different  matter, 
as  all  the  carbon  compounds  found  in  the  stack  gases  must 
originate  from  the  fuel.  As  already  seen,  carbon  dioxide,  (CO2), 
results  from  the  complete  combustion  of  carbon,  and  if  we  know 
the  ratio  between  the  volume  of  the  escaping  (C02)  and  the  total 
volume  of  the  products  carried  off  by  the  chimney,  we  shall  have 
quite  an  accurate  gage,  not  only  of  the  degree  of  combustion 
but  of  the  efficiency  of  the  furnace  as  a  steam  producer.  We  have 
already  noticed  that  danger  arises  from  excess  of  air  supply,  such 
excess  absorbing  and  carrying  off  the  heat  units  that  would  other- 
wise be  absorbed  by  the  heating  plates  of  the  boiler.  A  low  per- 
centage of  (CO2)  in  the  chimney  gases  may  be  due,  chiefly,  to 
incomplete  combustion,  or  it  may  be  due  in  a  large  measure  to 
a  high  percentage  of  air.  In  either  case  such  low  percentage 
would  be  indicative  of  corresponding  low  efficiency,  while  a  high 
percentage  of  the  gas  would  be  indicative  of  the  contrary. 

How  much  coal  is  wasted  when  the  percentage  of  (C02)  falls 
to  a  low  level  may  be  seen  by  a  glance  at  the  following  table. 

CO,  AND  FUEL  LOSSES. 


Pet. 
C0a 
15 

Pet.  Pre- 
ventable 
Fuel 
Loss 
0  0 

Pet. 
C02 
11  2 

Pet.  Pre- 
ventable 
Fuel 
Loss 
3  86 

Pet. 

C02 
74.. 

Pet.  Pre- 
ventable 
Fuel 
Loss 
11  70 

Pet. 

coa 

3  6 

Pet.  Pre- 
ventable 
Fuel 
Loss 
36  08 

14.8  . 

0  148 

11  0.. 

4.13 

7.2..  . 

.  .    12.34 

3.4. 

38.87 

14  6 

0  305 

10  8 

4  43 

70.. 

.  .    13  02 

3  2 

42  01 

14  4 

0  470 

10  6 

4  72 

6  8 

13  74 

3  0 

45  9g 

14  2 

0  635 

10  4 

5  03 

66... 

14  49 

2  8 

49  64 

14.0.. 

.  .  .  .      0.808 

10.2.. 

5.35 

6.4..  . 

.  .    15.30 

2  6 

54  34 

13  8 

0  990 

10  0  . 

.  .  .  .      569 

62.. 

16  16 

2  4 

60  32 

13.6.. 

1.17 

9.8.. 

6.04 

6.O..  . 

.  .    17.09 

2  2 

66  30 

13  4 

1  36 

9  6  . 

6  40 

58  

18  06 

2  0 

74  00 

13  2 

1  54 

9  4 

6  78 

5  6 

19  12 

1  8 

83  56 

13  0 

1  75 

9  2 

7  18 

54  

.    20  25 

1  6 

95  45 

12.8  . 

1.95 

9.O.. 

7.58 

5.2..  . 

.  .    21.47 

1  4 

12  6 

2  16 

8  8  . 

.  .  .  .      8  02 

5  0 

.    22  79 

1  2 

12  4 

2  38 

8  6 

8  47 

4  8 

24  21 

1  0 

12  2 

2  60 

8  4  . 

8  95 

46... 

.    25  76 

g 

12  0 

2  84 

8  2 

9  44 

4  4 

27  44 

6 

11.8.. 

...      3  08 

8  0.. 

9  66 

4.2  

.  .    29  29 

.4 

11  6  . 

3  33 

7  8  . 

10  51 

4  0 

31  28 

2 

11.4.. 

3.59 

7.6.. 

.    11.09 

3.8... 

00    CO 

COMBUSTION    AND   THE    BOILER    FURNACE  25 

If  combustion  is  incomplete,  the  following  gases  and  com- 
pounds may  be  found  among  the  escaping  chimney  gases: 

Hydrogen,  marsh  gas,  olefiant  gas,  benzine  compounds, 
ammonia,  water  vapor,  certain  compounds  of  nitrogen  and  sul- 
phur and  certain  hydrocarbon  compounds  of  the  type  of  marsh 
gas,  etc.  All  are  combustible  except  the  water. 

When  combustion  is  complete,  the  only  gases  and  compounds 
escaping  from  th§  chimney  are  nitrogen,  carbon  dioxide,  (C02), 
sulphur  dioxide, '  (S02) ,  and  water  vapor,  (H2O).  The  sulphur 
may  appear  in  compound  with  hydrogen  and  oxygen  as  sulphurous 
or  sulphuric  acid  vapor.  Carbon  dioxide  should  largely  pre- 
dominate over  all  of  the  other  gases  contained  in  the  chimney 
mixture,  excepting  the  nitrogen  and,  as  has  already  been  said,  the 
quantity  in  which  it  is  present  determines  the  efficiency  of  com- 
bustion. 

The  problem  before  the  engineer  who  desires  a  smokeless 
chimney,  and  the  highest  possible  degree  of  boiler  efficiency,  will 
now  appear  to  be  of  simple  solution  and  may  be  inferred  from 
what  has  already  been  pointed  out. 

Two  things  are  absolutely  necessary  for  the  complete  com- 
bustion of  bituminous  coal  and  its  gaseous  elements: 

1st.  The  introduction  of  air  in  the  proper  quantity,  and  at 
the  right  times,  and  in  such  a  manner  that  the  oxygen  contained 
in  the  air  will  freely  mingle  with  the  gases  as  fast  as  they  are  dis- 
tilled, and  promote  combustion. 

2d.  The  maintenance  of  the  gases  at  a  temperature  at  or 
above  their  igniting  points,  until  they  are  completely  consumed 
or  oxidized. 

Provision  must  also  be  made  for  the  expansion  of  the  gases 
during  the  period  of  their  combustion.  This  involves  details 
of  construction  that  will  be  touched  upon  at  the  proper  time. 

The  problem  is,  however,  not  so  simple  as  it  appears.  There 
are  serious  mechanical  difficulties  to  be  overcome,  in  order  to 
introduce  the  air  in  such  a  manner  that  more  benefit  than  harm 
will  result.  There  are  many  things  to  be  considered,  —  draft, 
grate  area,  coal  used,  methods  of  firing  employed,  etc.,  etc. 
The  same  combination  of  conditions  probably  never  obtains  in 
any  two  given  plants.  Conditions  are  moreover  constantly 
changing  in  the  same  plant.  Nice  judgment  will  be  required  on 
the  part  of  the  engineer,  or  fireman,  in  charge  of  the  boiler., 


26  COMBUSTION  AND  SMOKELESS   FURNACES 

reinforced,  in  the  case  of  a  hand-fired  furnace,  by  certain  auxiliary 
devices,  if  the  highest  results  are  to  be  expected. 

We  will  first  discuss  air  introduction.  Here  we  find  the  chief 
difficulties  and  problems  of  the  proposition.  If  the  air  question 
began  and  ended  with  supplying  oxygen  to  the  grates,  and  to 
the  gases  released  above  the  grates,  the  problem  would  be  simple 
of  solution.  The  fire-doors,  for  instance  might  be  left  open  or 
removed  entirely,  and  we  should  have  all  the  oxygen  required 
for  the  combustion  of  the  gases.  We  should,  however,  have  little 
or  no  steam.  Air  regulation  is  necessary,  and  proper  air  regula- 
tion presents  many  difficulties. 

A  great  deal  depends  upon  the  grate,  but  we  cannot  expect 
to  get  sufficient  free  oxygen  into  the  fire-box  by  way  of  the  grates. 
No  grate  has  ever  been  devised  that  will  meet  the  situation  pre- 
sented by  the  fire-box.  If  such  a  grate  were  possible,  no  means 
could  be  devised  to  regulate  the  amount  of  free  air  passing  through 
it.  The  bed  of  fuel  on  the  grates  will  be  at  times  relatively  thick, 
and  at  other  times  relatively  thin.  There  will  be  clinkers  at  times 
to  obstruct  the  flow  of  air,  and  at  other  times  there  will  be  air 
holes  or  fissures  in  the  fire.  The  fireman  can  exercise  some 
control  over  these  matters,  but  his  control  does  not  go  to  the 
extent  required  if  we  are  to  supply  air  to  the  gases  in  the  fire-box 
by  way  of  the  grates.  If  such  supply  were  possible  through  the 
grates,  what  means  could  we  employ  to  increase  and  diminish 
the  supply  to  meet  the  changing  circumstances  in  the  fire-box? 
Air  must  be  admitted  above  the  fire. 

Let  us  see  if  we  can  get  at  any  facts  that  will  enable  us  to 
determine  what  proportion  of  the  air  necessary  to  the  combustion 
of  our  fuel  must  be  given  to  the  grates,  and  what  proportion  to 
the  fire-box  for  admixture  with  the  gases. 

One  pound  of  fixed  carbon  requires  for  its  complete  combus- 
tion 2.65  Ib.  of  oxygen.  As  the  proportion  of  oxygen  and  ozone 
in  the  air  varies  somewhat  with  circumstances,  we  will  say, 
roughly  speaking,  that  12  Ib.  of  air  are  required  to  furnish  the 
necessary  oxygen. 

One  pound  of  hydrogen  requires  for  its  complete  combustion 
7.97  Ib.  of  oxygen,  or  in  the  neighborhood  of  36  Ib.  of  air. 

As  pointed  out  in  a  preceding  table,  a  pound  of  carbon  mo- 
noxide will  require  about  6  Ib.  of  air,  a  pound  of  olefiant  gas  15.43 
Ib.,  and  a  pound  of  marsh  gas  16.2  Ib. 


COMBUSTION    AND   THE    BOILER    FURNACE  27 

The  combined  efforts  of  a  chemist  and  a  mathematician  would 
seem  to  be  necessary,  if  we  are  to  determine  exactly  how  much 
air  to  deliver  to  the  grates  and  how  much  to  the  fire-box. 

The  authorities  appear  to  be  at  great  disagreement  over  this 
question.  One  tells  us  that  we  must  introduce  10  cu.  ft.  of  air 
into  the  fire-box  for  every  cubic  foot  of  gas  distilled.  Prof. 
Thurston,  of  Cornell  University,  says  in  his  "  Manual  of  the  Steam 
•  Boiler,"  that  from  10  to  15  per  cent,  of  the  air  supply  must  be 
delivered  above  the  grates.  Another  authority  advises  150  cu.  ft. 
of  air  above  the  grates  for  every  240  ft.  through  the  grates. 
They  should  tell  us  that  much  depends  upon  the  composition 
of  the  coal  and  other  circumstances,  and  that  no  rule  laid  down 
may  be  considered  as  applicable  to  all  cases. 

Other  authors  instruct  us  as  to  the  size  of  the  air  openings  that 
should  be  provided  entering  the  fire-box.  One  tells  us  that  an  air 
opening  of  from  one  to  six  square  inches  is  necessary  for  each 
square  foot  of  grate  surface,  and  that  the  openings  should  be 
increased  or  diminished  between  these  extremes  according  to 
the  speed  of  the  draft.  This  author  says  nothing  about  the 
amount  of  coal  consumed  per  hour  per  square  foot  of  grate,  and 
nothing  about  the  quality  of  the  coal.  Chas.  Wye  Williams,  in 
his  work  on  the  steam  boiler,  recommends  an  opening  of  one 
square  inch  for  each  900  Ib.  of  coal  burned  per  hour. 

Text-books  are  of  little  value  to  us  in  our  search  for  practical 
information  along  these  lines.  There  are  no  appliances  about 
the  boiler  room  for  weighing  air  and  gases,  and  if  there  were,  it 
would  be  difficult  to  employ  them  in  such  a  way  that  they  would 
assist  us  in  getting  the  right  amount  of  air  into  the  fire-box  at 
the  right  time.  The  matter  of  adjusting  the  air  supply  must  be 
determined  by  experiment  and  by  observation  of  the  flame  in 
the  fire-box.  Determination  of  the  character  of  the  flue  gases 
—  the  percentage  of  .carbon  dioxide,  etc.  —  will  also  be  of  great 
practical  assistance.  Instruments  for  this  purpose  are  available 
and  comparatively  inexpensive.  They  should  be  a  part  of  the 
equipment  of  every  well  conducted  steam  plant.  Actual  experi- 
ment, or,  to  use  a  homely  phrase, "  a  process  of  cutting  and  fitting," 
is  the  only  means  available  for  determining  these  questions  in 
specific  cases.  Theoretical  generalizations  and  mathematical 
formulas  are  beautiful  things  in  their  way,  but  they  are  of 
little  practical  use  to  the  engineer.  Every  steam  boiler  has 


28  COMBUSTION   AND  SMOKELESS   FURNACES 

its  own  peculiarities  and  must  be  dealt  with  as  a  separate  propo- 
sition. 

Much  will  be  found  to  depend  upon  the  size,  shape,  and  location 
of  the  air  passages  leading  into  the  fire-box,  and  the  temperature 
of  the  air  introduced.  When  we  are  considering  the  size  and 
shape  of  the  air  passages,  the  element  of  friction  must  be  con- 
sidered, as  it  tends  to  greatly  retard  the  speed  of  the  air  currents 
passing  through.  Frictional  surface  rapidly  increases  in  propor- 
tion to  area  as  the  size  of  the  passages  is  diminished.  Suppose, 
for  example,  we  are  delivering  air  to  the  fire  through  one  pipe, 
4  in.  in  diameter,  and  we  decide,  in  order  to  get  better  air  dis- 
tribution, to  increase  the  number  of  pipes  or  inlets.  What  must 
be  the  diameters  of  the  smaller  pipes,  and  the  number  of  them, 
in  order  that  we  may  deliver  an  amount  of  air  equivalent  to  that 
carried  by  the  4-in.  pipe?  If  we  make  these  smaller  pipes  3  in.  in 
diameter,  we  shall  require  2.3  pipes,  if  2  in.  in  diameter,  5.7  pipes, 
and  if  1  in.  in  diameter,  32  pipes.  More  air  will  pass  through 
a  round  opening  than  through  a  square  or  angular  opening  of  the 
same  area,  for  the  reason  that  there  is  less  frictional  surface. 

The  location  of  the  air  inlets  is  a  consideration  of  great  im- 
portance. If  the  inlets  are  so  arranged  that  the  air  when  intro- 
duced into  the  fire-box  will  mingle  readily  with  the  gases,  we 
shall  be  able  to  get  combustion  with  a  smaller  surplus  of  air  than 
otherwise.  This  stands  to  reason.  If,  for  instance,  air  is  de- 
livered into  the  fire-box  through  the  side  walls,  the  air  currents, 
as  soon  as  they  enter,  are  caught  in  the  draft  of  the  furnace  and 
carried  back  over  the  bridge  wall  along  the  side  walls  of  the  boiler 
setting.  It  is  manifest  that  if  the  gases  in  the  center  of  the  fire- 
box are  to  receive  any  oxygen,  a  large  surplus  of  air  must  be  in- 
troduced, if  such  introduction  is  through  the  side  walls. 

If  the  air  is  introduced  above  the  fire,  mixture  with  the  gases 
will  take  place  more  readily  and  more  intimately.  The  air  being 
colder,  and  consequently  heavier  than  the  gases,  will  tend  to 
settle,  while  the  gases,  on  the  other  hand,  will  be  disposed  to  rise. 
The  result  will  be  an  intermingling.  If,  on  the  other  hand,  the 
air  is  delivered  into  the  fire-box  through  openings  in  the  bridge 
wall,  it  will  enter  below  the  gas  currents,  and  the  bulk  of  it  will 
remain  there  until  the  tubes  are  reached.  By  this  time  the  gases 
will  probably  have  chilled  to  a  point  where  the  oxygen  will  be 
able  only  imperfectly  to  perform  its  office,  if  at  all. 


COMBUSTION    AND   THE    BOILER    FURNACE  29 

The  temperature  of  the  air  admitted  is  another  matter  re- 
quiring consideration.  It  is  obvious  that  the  air  and  gases,  upon 
intermingling,  must  strike  a  common  level  as  to  temperature. 
The  colder  the  air,  the  lower  will  be  the  temperature  of  the  mix- 
ture and  the  lower  the  net  degree  of  heat  resulting  from  the  com- 
bustion of  the  gases.  The  air,  if  colder  than  the  gases,  will  absorb 
a  certain  number  of  heat  units  which  are  thus  incapacitated  from 
performing  any  offices  in  steam  generation.  "Heat  aids  all 
chemical  action,"  and  the  hotter  the  air  admitted,  the  more 
intimate  will  be  the  association  of  the  oxygen  with  the  fuel,  and 
the  smaller  will  be  the  quantity  of  the  air  required.  The  smaller 
the  air  surplus,  the  greater  will  be  the  efficiency  of  the  boiler. 

We  must  not  lose  sight  of  the  fact  that  air  expands  when 
heated,  and  that  it  is  the  weight  of  air  employed  in  combustion 
that  does  the  work  and  not  the  volume.  Let  us  see  to  what 
extent  air  and  gas  expand  when  heated.  Suppose  we  take  air 
at  a  temperature  of  62  deg.  F.,  one  pound  of  it  will  occupy  13.141 
cu.  ft.  At  100  deg.  it  will  occupy  14.096  cu.  ft.;  at  500  deg.  it 
will  occupy  24.146  cu.  ft.,  and  at  1000  deg.  36.811  cu.  ft.  At 
3000  deg.  the  air  will  be  expanded  to  87.13  cu.  ft.  We  might 
easily  heat  the  air  to  500  deg.  before  delivery  to  the  fire-box,  and 
in  such  event  the  air  inlets  would  have  to  be  of  substantially 
double  the  capacity  required  at  a  temperature  of  62  deg.  If 
changes  are  made  with  a  view  of  increasing  the  air  supplied  to 
the  fire-box,  it  may  be  advisable  to  lower  the  bridge  wall  to  some 
extent,  and  perhaps  make  other  alterations,  with  a  view  of  ac- 
commodating the  increased  volume  of  gases.  Suppose  the  tem- 
perature of  the  fire-box  is  2000  deg.,  and  we  admit  more  air.  A 
pound  of  air  at  2000  deg.  will  be  expanded  to  occupy  61.94  ft. 
Unless  extra  space  is  provided  for  the  accommodation  of  this  air, 
between  bridge  wall  and  boiler,  retardation  of  the  draft  is  likely 
to  result. 

We  have  yet  to  deal  with  the  most  difficult  of  the  problems 
presenting  themselves,  when  we  undertake  the  regulation  of  the 
air  supply  entering  the  fire-box.  Before  approaching  this  prob- 
lem, we  will  first  make  some  preliminary  observations.  The 
familiar  "Welsbach,"  or  mantle  gas  light,  suggests  some  ideas. 
When  the  air-regulating  mechanism  below  the  mantle  is  properly 
adjusted,  combustion  of  the  gas  is  complete,  and  the  flame  and 
mantle  are  incandescent.  If  we  reduce  the  air  supply,  com- 


30  COMBUSTION  AND  SMOKELESS   FURNACES 

bustion  is  incomplete,  and  we  have  flame  and  gas  at  the  top  of 
the  mantle.  If  too  much  air  is  admitted,  the  light  "dies  down," 
the  surplus  air  cooling  the  mantle  to  a  point  where  a  high  degree 
of  incandescence  is  impossible.  Correct  adjustment  of  the  air 
supply  means  the  brightest  light  and  the  greatest  economy  in 
the  consumption  of  gas.  What  is  the  character  of  the  gas  we  are 
burning  in  the  mantle  light?  It  is  coal  gas,  —  the  same  gas  that 
we  find  in  the  furnace  of  the  steam  boiler,  with  some  of  the  im- 
purities eliminated.  We  would  emphasize  the  observation  that 
correct  adjustment  of  the  air  supply  is  as  essential  to  the  boiler 
furnace  as  it  is  to  the  gas  light.  If  we  give  the  gases  in  the  fur- 
nace too  little  air,  we  have  smoke,  just  as  in  the  case  of  the  gas 
light.  If  we  introduce  too  much  air,  the  plates  of  the  boiler  are 
cooled  and  steam  "dies  down,"  just  as  the  incandescence  of  the 
mantle  disappears.  In  these  respects  the  two  cases  are  similar, 
but  the  difficult  problem  we  have  in  mind  applies  to  the  steam 
boiler  furnace,  and  not  at  all  to  the  mantle  gas  light.  In  the 
case  of  the  mantle  light,  we  have  a  uniform  pressure  and  supply 
of  gas,  or  substantially  so.  Once  the  air  supply  is  adjusted  it 
requires  no  further  attention.  The  situation  is  entirely  different 
with  the  steam  boiler  furnace.  Here  the  volume  of  gas  fluctu- 
ates between  wide  extremes  and  the  demand  for  air  fluctuates 
accordingly.  There  is  a  large  volume  of  gas  immediately  after 
firing  the  furnace  with  fresh  coal.  This  volume  gradually  dimin- 
ishes until  the  coal  is  coked,  when  the  volume  of  combustible  gas 
is  comparatively  very  small  and  remains  so  until  the  next  firing. 
Now,  unless  means  can  be  devised  to  suit  the  air  supply  to  the 
changing  requirements,  we  may  perhaps  be  better  off,  from  a 
point  of  economy,  if  we  make  no  attempts  at  all  to  add  to  the 
air  supply  of  the  fire-box.  Fig.  2  will  serve  to  graphically  illus- 
trate the  contentions  of  the  writer  in  this  connection. 

We  will  let  the  letter  "  D,"  in  the  diagram,  indicate  the  point 
at  which  the  furnace  is  fired  with  fresh  coal,  and  the  black  triangle 
the  volume  of  smoke  and  gas  that  is  emitted  in  evidence  of  the 
incomplete  combustion  of  the  volatile  matter.  This  volume  of 
smoke  and  gas  diminishes  gradually  from  the  point  of  maximum 
density,  reached  soon  after  firing,  to  the  point  "C,"  where  the 
coal  is  completely  coked  and  smoke  entirely  disappears.  The 
stack  then  remains  clear  until  the  next  firing,  although  a  small 
quantity  of  invisible  coke  gas  may  be  escaping.  When  the  fur- 


COMBUSTION    AND   THE    BOILER   FURNACE 


31 


nace  is  again  stoked,  the  process  is  repeated.  The  space  marked 
"t"  will  accordingly  represent  the  time  that  elapsee  between 
the  firing  of  the  furnace  and  the  coking  of  the  coal,  —  the  time 
during  which  smoke  issues.  "A"  will  represent  the  maximum 
supply  of  air  demanded,  which  is  the  amount  required  to  burn 
the  maximum  amount  of  smoke  or  gas  emitted.  The  dotted 
line  "a,"  "a,"  "a,"  represents  the  correct  air  supply  at  all  the 
different  stages  between  the  times  of  firing  the  furnace.  The 
maximum  supply  of  air  should  be  admitted  as  soon  as  the  opera- 
tion of  stoking  the  furnace  is  completed.  This  supply  should 
be  gradually  reduced,  and  reaeh  its  minimum  when  the  coal  is 
entirely  coked.  It  should  remain  at  the  minimum  until  the  next 
firing.  The  minimum  supply  should  be  such  an  amount  as  is 
sufficient  to  burn  the  carbon  monoxide,  or  coke  gas,  given  off 


FIG.  2 

from  the  incandescent  fuel.  Now,  if  we  merely  provide  for  such 
an  air  supply  as  would  be  sufficient  to  oxidize  the  maximum 
volume  of  gas;  (and  such  provision  must  be  made  if  we  are  to  have 
a  smokeless  chimney),  neglecting  provision  for  the  gradual  re- 
duction of  this  supply  to  meet  the  changing  requirements  of  the 
fire-box,  we  should  have  the  situation  indicated  by  the  dotted 
line,  "B,"  "B,"  in  the  diagram.  We  should  be  filling  the  space 
"A,"  "C,"  «T>,"  "A,"  with  surplus  air,  every  cubic  foot  of  which 
would  be  robbing  the  boiler  of  heat  units.  We  might  be  getting 
complete  combustion,  which  in  itself  would  mean  a  gain  in  effi- 
ciency, but  we  should  be  fortunate  if  the  surplus  air  admitted 
would  not  cause  a  loss  sufficient  to  more  than  overbalance  the 
gain  made.  The  boiler  furnace  presents  all  of  the  problems  of 


32  COMBUSTION  AND  SMOKELESS  FURNACES 

the  mantle  gas  light,  with  the  additional  problems  of  maximum 
and  minimum  supplies,  and  air  reduction,  added. 

Common  sense  will  support  all  of  the  above  contentions  in 
respect  of  air  regulation.  High  engineering  authorities  may  be 
cited  if  necessary. 

Washington  Jones,  who  may  be  considered  an  authority,  in 
a  contribution  on  Smoke  Prevention,  published  in  the  Journal 
of  the  Franklin  Institute,  Vol.  CXLIV,  p.  38,  says: 

"A  furnace,  immediately  after  a  fresh  supply  of  fuel,  requires 
more  than  double  the  quantity  of  air  it  did  the  instant  before, 
whilst  we  have  no  contrivance  for  furnishing  such  a  supply, 
although  without  it  throughout  the  space  of  time  during  which 
rapid  gasification  of  the  hydrogenous  portion  is  going  on,  more 
than  half  the  fuel  consumed  is  wasted  and  passes  off  unburnt, 
becoming  thereby  not  only  totally  unproductive  itself,  but  ab- 
solutely an  agent  of  evil,  robbing  the  furnace  of  the  heat  absorbed 
in  its  own  volatilization.  All  the  authorities  agree  in  this  dictum, 
*  After  a  fresh  supply  of  fuel  is  placed  upon  the  grate,  air  must 
be  admitted  above  the  grate  and  its  volume  regulated  by  a 
damper."5 

In  his  "Manual  of  Steam  Boilers/'  p.  205,  Professor  Thurston 
says: 

"Attempts  to  improve  the  efficiency  of  a  heat-generating 
apparatus  by  'burning  the  smoke7  usually  fail  by  introducing 
such  an  excess  of  air  as  to  cause  a  loss  exceeding  that  before 
experienced  from  the  formation  of  smoke.  Thorough  inter- 
mixture of  a  minimum  supply  of  air  with  the  gases  distilled  from 
the  fuel  is  the  only  means  of  attaining  high  efficiency." 

Economy  considered,  regulation  of  the  air  supply  entering 
the  fire-box  is  just  as  important  as  regulation  of  the  steam  sup- 
plied to  the  cylinder  to  meet  the  load  carried  by  the  engine. 
Some  ingenuity  may  be  necessary  to  accomplish  such  regulation, 
but  the  stakes  are  sufficiently  large  to  justify  almost  any  amount 
of  outlay  and  effort  required. 

It  is  directly  to  the  point  to  inquire  what  may  be  the  extent 
of  the  loss  in  case  of  incomplete  combustion.  The  writer  will 
support  his  views  by  further  quotations  from  standard  authorities. 

In  Thurston's  "Manual  of  Steam  Boilers,"  p.  189,  will  be  found 
a  report  of  an  exhaustive  and  scientific  test,  made  for  the  pur- 
pose of  determining  the  amount  of  waste  resulting  from  the 


COMBUSTION    AND   THE    BOILER    FURNACE  33 

incomplete  combustion  of  the  gaseous  elements  of  bituminous 
coal.  A  steam  boiler  equipped  for  service  operation  was  em- 
ployed in  the  tests.  In  summing  up  his  comments  upon  these 
tests,  Professor  Thurston  says: 

"The  transformation  of  a  mass  of  black  smoke  into  a  flame 
many  feet  in  length  is  the  best  possible  evidence  of  the  advantage 
of  this  operation.  The  gain  in  economy  of  fuel  was  estimated 
at  about  one  third  when  the  supply  of  air  was  properly  adjusted 
and  managed." 

On  page  186  of  the  same  work  Professor  Thurston  says: 

"The  highest  efficiency  of  heat  production  is  secured  by 
perfect  combustion  with  the  least  practicable  air  supply,  obtain- 
ing the  highest  possible  resulting  temperature." 

And  again  on  page  205  we  find  Thurston  expresses  himself: 

"With  too  thin  a  fire  the  danger  arises  of  excess  of  air  sup- 
ply; with  too  thick  a  fire,  carbon  monoxide  may  be  produced. 
In  the  former  case,  combustion  will  be  complete,  but  the  heat 
generated  will  be  distributed  throughout  the  diluting  excess  of 
air,  and  thus  rendered  less  available  and  the  efficiency  of  the 
furnace  correspondingly  reduced,  while  in  the  latter  case  a  loss 
arises  from  incomplete  combustion,  and  waste  takes  place  by 
the  passage  of  combustible  gas  up  the  chimney." 

Professor  Rankine,  of  the  University  of  Glasgow,  is  an  author- 
ity of  such  weight  that  he  is  frequently  quoted  in  the  works  of 
Professor  Thurston.  In  his  "Manual  of  the  Steam  Engine,"  p. 
291,  Professor  Rankine  says: 

"The  greatest  probable  amount  of  waste,  when  the  absence 
of  any  provision  for  introducing  air  to  burn  the  inflammable 
gases  is  combined  with  bad  firing,  may  be  estimated  by  taking 
the  proportion  in  which  the  total  heat  of  the  combustion  of  the 
coke  or  fixed  carbon  contained  in  one  pound  of  coal  is  less  than 
the  total  heat  of  combustion  of  all  the  constituents  of  one  pound 
of  coal." 

This  would  seem  to  mean  that  conditions  are  possibly  so  bad 
as  to  result  in  a  total  loss  of  all  of  the  volatile  fuel  contained  in 
the  coal.  Now  let  us  see  what  Professor  Rankine  would  estimate 
as  the  probable  percentage  of  loss  under  such  circumstances. 

Taking  reliable  analyses  of  the  coals  produced  by  ten  random 
Illinois  counties,  and  computing  the  averages,  we  find  the  heat 


34  COMBUSTION  AND  SMOKELESS   FURNACES 

value  to  be  10,670  British  thermal  units  per  pound  of  coal.  We 
also  find  that  these  coals  contain  an  average  of  48.484  per  cent, 
fixed  carbon.  One  pound  of  carbon,  as  has  been  seen,  contains 
14,540  British  thermal  units;  48.484  per  cent,  of  14,540  gives  us 
7049  British  thermal  units  residing  in  the  fixed  carbon.  Invok- 
ing Professor  Rankine  and  subtracting  7049  ("the  total  heat  of 
combustion  of  the  coke  or  fixed  carbon  contained  in  one  pound 
of  coal")  from  10,670  ("the  total  heat  of  combustion  of  all  the 
constituents  of  one  pound  of  coal"),  we  get  a  balance  of  3621 
British  thermal  units.  This  is  33.926  per  cent,  of  the  energy,  or 
fuel  value  of  the  coal,  and  Professor  Rankine  says  that  it  is  pos- 
sible to  operate  a  plant  along  such  unscientific  lines  that  this 
amount  —  the  entire  volatile  element  of  the  fuel  —  will  pass 
up  the  chimney  and  be  lost. 

Hollis  W.  Field  is  responsible  for  the  following  statements: 

"When  soft  coal  of  any  class  is  burned  in  a  way  to  spread  a 
cloud  of  smoke  around  the  top  of  the  stack,  to  the  point  of  making 
a  nuisance  of  the  plant,  nearly  three  times  more  energy  is  going 
out  of  the  flue  than  is  given  to  the  main  belt  at  the  fly-wheel, 
and  when  the  stack  is  smoking,  as  so  many  stacks  do  smoke,  it 
may  be  figured  that  a  good  dividend  on  a  large  block  of  stock 
in  the  concern  is  going  out  into  the  upper  air  every  thirty  days. 

"But  considering  that  the  coal  has  been  shoveled  in  to  the 
best  advantage  known  to  modern  practice,  there  will  be  a  small 
cloud  only,  at  the  top  of  the  stack,  and  yet  in  this  vaporous  dis- 
charge of  smoke,  not  nearly  approaching  the  need  of  a  smoke 
inspector,  2970  units  of  the  14,540  will  be  discharged  as  a  waste 
that  is  impossible  of  recovery  in  any  form.  This  is  almost  one 
fifth  of  the  possibilities  of  the  coal  under  the  best  that  can  be 
done;  when  a  stack  is  hooded  for  half  its  length  in  a  dense  nimbus 
of  coal  smoke,  perhaps  half  of  the  value  of  the  coal  in  the  fire- 
box has  escaped  in  carbon  and  in  gases." 

Some  interesting  conclusions  can  be  deduced  from  the  follow- 
ing figures,  which  are  taken  from  good  engineering  authorities: 

The  efficiency  of  a  furnace  and  boiler  is  reckoned  from  the 
proportion  that  the  heat  absorbed  by  the  boiler  bears  to  the  total 
heat  units  contained  in  the  coal.  It  requires  a  good  boiler  of  the 
multitubular  type,  and  fair  conditions  of  operation,  to  show  an 
efficiency  of  60  per  cent.  This  leaves  40  per  cent,  of  waste  to  be 
accounted  for.  The  escaping  stack  gases  will  probably  have  a 
temperature  of  600  deg.,  and  this  waste  of  heat  units  released  in 


COMBUSTION  AND  THE  BOILER  FURNACE  35 

the  furnace  will  approximate  about  22  per  cent.  A  portion  of 
this  loss  is  preventable  and  may  be  charged  to  the  heating  of 
unnecessary  excess  air.  Probably  2  per  cent,  of  the  fuel  will  be 
lost  through  the  grates  and  4  or  5  per  cent,  of  the  heat  will  be 
lost  by  radiation.  This  leaves  a  balance  of  around  12  per  cent, 
that  we  are  at  a  loss  to  account  for  in  figuring  up  a  "heat  bal- 
ance. "  Many  engineers  charge  the  "unaccounted  for"  loss  to 
Methane  and  other  hydro-carbon  gases.  Much  remains  to  be 
learned  about  what  really  takes  place  in  a  furnace  burning  a 
complex  hydro-carbon  fuel. 

The  following  conclusions  must  be  drawn: 

First,  that  "smoke  means  waste;"  second,  that  under  right 
conditions  smoke  may  be  consumed  or  "prevented;"  third,  that 
smoke  may  be  burned  or  prevented  without  securing  an  increase 
in  efficiency — that  smokeless  combustion  does  not  necessarily 
mean  economical  combustion;  fourth,  that  complete  combustion, 
coupled  with  proper  air  regulation,  means  a  large  saving  of  fuel 
and  that  if  combustion  is  improved  without  such  saving  the 
fault  may  be  charged  to  improper  regulation  of  the  air  entering 
the  firebox. 

The  direct  fuel  wastes  attributable  to  "smoke"  have  been 
greatly  overestimated  by  many  writers.  There  may  be  a  great 
deal  of  "smoke"  and  very  little  of  fuel  value  going  up  the  chim- 
ney, or  there  may  be  very  little  smoke  and  a  great  deal  of  waste 
combustible  in  the  chimney  gases. 

Low  boiler  settings  explain  more  smoke  than  any  other  one 
cause,  and  where  smoke  is  caused  by  the  snuffing  out  of  the  flame 
upon  a  cold  surface,  as  in  the  case  of  a  low  set  boiler,  there  may 
be  no  trace  of  combustible  gas  in  the  floating  soot.  The  fuel  lost 
in  the  soot  itself  is  almost  negligible.  The  fuel  lost  through  the 
insulating  effect  of  soot  on  the  heating  surfaces  is  not  negligible 
by  any  means.  It  is  a  serious  loss.  Soot  ranks  away  ahead  of 
asbestos  as  an  insulating  material.  The  slightest  coating  of  it 
upon  the  tubes  or  heating  surfaces  of  a  boiler  will  cause  a  marked 
difference  in  the  coal  consumption.  The  loss  is  not  so  much  in 
the  soot  that  goes  up  the  chimney.  It  is  in  the  soot  that  sticks 
to  the  boiler  and  does  not  go  up  the  chimney. 

Author's  Note: — For  a  further  discussion  of  Soot,  see  Ap- 
pendix. 


CHAPTER   III 

COMBUSTION    AND    THE    STEAM    BOILER 

THE  steam  boiler  in  its  relation  to  the  boiler  furnace,  and  the 
combustion  of  fuel  therein,  must  have  some  attention  before  we 
pass  on  to  a  direct  discussion  of  the  smoke  evil  and  the  devices 
that  are  being  offered  to  accomplish  its  suppression. 

The  boiler  usually  interposes  some  obstacles  in  the  way  of 
attaining  complete  combustion.  These  obstacles  vary  in  their 
nature  with  different  types  of  boilers.  We  must  understand 
wherein  the  difficulties  lie;  we  must  also  know  the  peculiarities 
of  the  various  styles  of  boilers  in  common  use,  so  far  at  least  as 
such  peculiarities  have  a  bearing  on  the  subject  of  combustion. 

What  are  the  requirements  of  a  good  boiler?  Let  us  consult 
an  authority.  Professor  Thurston,  who  has  already  been  quoted, 
gives  us  a  list  of  the  requirements  in  the  order  of  what  he  con- 
siders their  relative  importance.  They  are  as  follows: 

A  good  boiler  must  be  adapted  and  the  builder  should  be 
required, 

"  1st.  To  secure  complete  combuston  of  the  fuel,  without 
permitting  dilution  of  the  products  of  combustion  by  excess 
of  air." 

"2d.  To  secure  as  high  temperature  of  the  furnace  as 
possible." 

"3d.  To  so  arrange  heating  surfaces  that,  without  checking 
draft,  the  available  heat  shall  be  most  completely  taken  up  and 
utilized." 

"4th.  To  make  the  form  of  boiler  such  that  it  shall  be  con- 
structed without  mechanical  difficulty  or  excessive  expense." 

"5th.  To  give  it  such  form  that  it  shall  be  durable  under 
the  action  of  the  hot  gases  and  of  the  corroding  elements  of  the 
atmosphere." 

"6th.  To  make  every  part  accessible  for  cleaning  and  re- 
pairs." 

"7th.  To  make  every  part,  as  nearly  as  possible,  uniform 
in  strength  and  in  liability  to  loss  in  strength  by  wear  and  tear, 

36 


COMBUSTION  AND  THE  STEAM   BOILER  37 

so  that  the  boiler  when  old  shall  not  be  rendered  useless  by  local 
defects." 

"8th.  To  adopt  a  reasonably  high  factor  of  safety  in  pro- 
portioning." 

"9th.  To  provide  efficient  safety  valves,  steam  gages,  and 
other  appurtenances." 

"  10th.     To  secure  intelligent  and  very  capable  management." 

The  first  two  requisites,  only,  come  within  the  purview  of  our 
discussion.  That  they  are  placed  at  the  head  of  the  list  would 
seem  to  indicate  their  supreme  importance. 

We  will  quote  further  from  Professor  Thurston,  as  we  know 
of  no  higher  authority: 

"In  securing  complete  combustion  an  ample  supply  of  air 
and  its  thorough  intermixture  with  the  combustible  elements 
of  the  fuel  are  essential;  for  high  temperature  of  furnace  it  is 
necessary  that  the  air  supply  shall  not  be  in  excess  of  that  actually 
needed  to  give  complete  combustion.  The  efficiency  of  a  furnace 
burning  fuel  completely  is  measured  by  the  formula 


in  which  E  represents  the  ratio  of  heat  utilized  to  the  whole 
calorific  value  of  the  fuel;  T  is  the  furnace  temperature;  T'  the 
temperature  of  the  chimney,  and  t  that  of  the  external  air.  Hence, 
the  higher  the  furnace  temperature,  and  the  lower  that  of  the 
chimney,  the  greater  the  proportion  of  available  heat." 

Boiler  builders  as  a  rule  have  given  attention  to  the  third 
requisite  at  the  expense  of  the  first  two.  How  this  has  come 
about  will  be  better  understood  if  we  follow  briefly  the  evolution 
of  the  steam  boiler  from  its  primitive  forms  to  the  modern  types. 

James  Watt  was  among  the  first  to  make  use  of  a  steam  boiler 
for  power  purposes.  The  style  first  adopted  by  Watt  came  to 
be  known  as  the  "wagon"  boiler,  owing  to  its  general  resem- 
blance in  shape  to  a  wagon  with  a  canvas  cover.  The  boiler  was 
provided  with  a  passage  for  flame  and  gases,  beneath  the  plates, 
throughout  its  entire  length,  and  with  passages  for  similar  pur- 
poses at  the  sides.  The  "wagon"  boiler  gave  place  to  the  plain 
cylindrical  form. 

The  desirability  of  more  heat  absorbing  surface  soon  became 
apparent  to  the  early  boiler  builders,  and  what  is  known  as  the 


38  COMBUSTION  AND  SMOKELESS   FURNACES 

" Cornish"  boiler  was  the  first  result  of  the  efforts  in  this  direction. 
This  type  is  provided  with  a  large  return  flue,  running  throughout 
the  length  of  the  boiler.  This  was  soon  improved  upon  by  twin 
flues,  in  the  type  known  as  the  "Lancashire"  boiler.  The  result 
of  these  modifications  was  such  an  increase  in  efficiency,  that  the 
flues  idea  was  shortly  carried  to  the  extreme  of  development. 
The  return  tubular  boiler,  as  we  have  it  to-day,  is  a  direct  descend- 
ant of  the  early  " Cornish"  boiler. 

It  was  soon  conceived  that  a  furnace  placed  within  the  boiler 
would  expose  more  heating  surface  than  if  located  beneath  the 
boiler  shell.  The  internally  fired  boiler  is  an  outgrowth  of  this 
conception.  The  furnace  and  ash-pit  are  placed  within  a  large 
flue,  which  is  completely  surrounded  by  water.  A  conspicuous 
example  of  this  type  is  the  "marine"  boiler,  largely  employed 
upon  steam  vessels  owing  to  the  relatively  small  space  occupied 
and  the  absence  of  any  necessity  for  a  setting  of  masonry.  The 
steamer  is  usually  followed  by  a  dense  cloud  of  smoke,  which  is 
directly  chargeable  to  the  influence  of  the  cold  surfaces  of  the 
"marine"  boiler  upon  the  burning  gases.  Such  a  desideratum 
as  complete  combustion  is  out  of  the  question  where  one  of  the 
main  requirements  of  combustion  is  sacrificed  to  heating  surface. 

The  first  water-tube  boiler  made  its  appearance  in  1793.  This 
type,  in  late  years,  appears  to  be  increasing  in  popularity.  Among 
the  other  advantages  claimed,  is  large  heating  surface  and  pro- 
vision for  the  rapid  circulation  of  water. 

Having  shown  that  the  first  and  second  requisites  have  been 
sacrificed,  in  the  evolution  of  the  steam  boiler,  for  the  benefit  of 
the  third,  we  will  look  a  little  more  closely  at  the  modern  types. 
Steam  boilers  are  usually  classified  as  "stationary,"  "locomotive," 
and  "marine."  For  our  purposes  we  will  adopt  two  general 
classifications,  "externally  fired"  and  "internally  fired."  Loco- 
motive and  marine  boilers  will  of  course  be  included  in  the  second 
classification.  Most  water-tube  boilers  will  class  as  externally 
fired.  We  must,  however,  adopt  a  sub-classification  for  the 
water-tube  type,  as  those  conducting  the  gases  directly  to  the 
tubes  present  problems  as  to  combustion  not  offered  by  those 
first  conducting  the  gases  into  a  combustion  chamber  after  the 
manner  of  the  return-tubular  boiler. 

As  we  have  already  dealt  to  some  extent  with  the  externally 
fired  return-tubular  boiler,  little  further  need  be  said  at  this 


COMBUSTION  AND  THE  STEAM  BOILER 


39 


juncture  concerning  it.  The  result  of  bringing  the  burning  gases 
too  soon  into  contact  with  the  cold  boiler  shell  was  pointed  out 
in  connection  with  the  illustration,  Fig.  1. 

The  type  of  water-tube  boiler  that  conducts  the  gases  at  once 
among  the  tubes  offers  great  obstacles  to  the  completion  of 
combustion  and  is  usually  a  bad  "  smoker."  We  have  already 
shown  that  the  burning  gases  must  have  opportunity  for  expan- 
sion while  in  a  state  of  combustion.  Such  opportunity  is  almost 
entirely  lacking  in  the  type  now  being  considered.  The  bridge 
wall  rises  into  contact  with  the  water  tubes,  and  the  tile  baffle 
plates  between  the  tubes  are  arranged  in  vertical  formations. 
The  burning  gases  rise  vertically  from  the  fire-box,  and  are  at 
once  in  contact  with  the  cold  surfaces  of  the  water  tubes.  The 
elements  of  time  and  space,  necessary  to  the  completion  of  com- 


FIG.  3 


FIG.  4 


bustion,  are  both  lacking.  There  may  be  good  grounds  for  the 
arguments  usually  advanced  in  favor  of  such  a  boiler,  —  viz., 
that  it  offers  superior  circulation  of  water  through  the  tubes, 
owing  to  the  application  of  the  greater  degree  of  heat  near  the 
point  where  the  tubes  enter  the  water  legs;  that  the  gases  are 
brought  earlier  into  contact  with  the  tubes,  and  a  greater  degree 
of  heat  extracted  than  would  otherwise  be  possible,  etc.  We 
have  no  concern  with  these  arguments,  as  our  province  is  limited 
to  combustion.  Having  combustion  and  smoke  elimination  in 
mind,  the  only  hope  of  satisfactory  results  where  such  a  boiler 
is  employed  lies  in  what  is  commonly  termed  a  " Dutch  oven" 
furnace,  exterior  to  the  boiler  proper  and  its  setting,  and  the  use 
of  the  space  occupied  by  the  furnace  and  ash-pit  of  the  boiler, 


40  COMBUSTION   AND  SMOKELESS   FURNACES 

as  a  combustion  chamber.  This  type  of  boiler  is  partially  illus- 
trated in  Fig.  3,  and  the  application  of  the  "Dutch  oven"  sug- 
gested in  Fig.  4.  There  are  a  number  of  objections  to  the  use  of 
a  "Dutch  oven/'  to  which  we  will  call  attention  later. 

With  the  water-tube  boiler  employing  a  combustion  chamber 
at  the  rear  of  the  bridge  wall,  the  same  arguments  apply  as  in 
the  case  of  the  return-tubular  boiler.  In  this  type  the  baffle 
plates  are  disposed  between  the  tiers  of  tubes  and  parallel  with 
them,  the  gases  being  first  conducted  through  the  combustion 
chamber  and  then  up,  for  circulation  among  the  tubes.  If  what 
is  known  as  "enveloping  tile"  are  employed  upon  the  lower  tier 
of  tubes,  considerable  assistance  will  be  rendered  to  combustion, 
chilling  contact  of  the  gases  with  the  cold  tubes  being  thereby 
avoided. 

"Dutch  oven"  furnaces  can  also  be  employed,  with  good 
results  as  to  combustion,  in  the  case  of  all  internally-fired  boilers. 
Such  expedient  is,  in  fact,  about  the  only  resource  in  such  cases, 
if  anything  approaching  complete  combustion  is  desired. 

There  is  a  growing  tendency  to  give  combustion  more  of  a 
chance  by  giving  the  furnace  more  space.  The  most  active  of  all 
the  causes  of  smoke  is  lack  of  space.  The  old  theory  seemed  to  be 
that  there  should  be  just  room  enough  between  the  boiler  and 
the  grates  to  permit  building  a  fire.  We  are  getting  away  from 
that  idea.  What  is  known  as  the  " Hartford  specification"  for 
the  setting  of  return  tubular  boilers  called  for  a  distance  of  28 
inches  between  the  grates  and  the  shell  of  the  boiler.  That 
specification  is  still  being  followed,  bad  as  it  is.  In  fact,  it  is 
quite  unusual  to  find  a  boiler  of  the  return  tubular  type  set  in 
any  other  manner.  Any  boiler  so  set  with  an  ordinary  furnace 
will  cause  smoke  and  a  lot  of  it. 

A  prominent  boiler  insurance  company  has  just  issued  a 
specification  for  the  setting  of  return  tubular  boilers.  It  calls 
for  a  distance  of  48  inches  between  the  boiler  shell  and  the  grates. 
This  is  none  too  much.  In  a  New  York  power  station  the  tubes 
of  the  water  tube  boilers  are  15  feet  from  the  grates. 

The  man  with  the  smokeless  furnace  to  sell  will  find  a  poor 
field  for  his  activities  when  we  learn  how  to  build  furnaces  and 
set  boilers  that  are  suited  to  the  burning  of  bituminous  coal. 


CHAPTER  IV 
"THE  CHIMNEY  EVIL" 

THE  smoke  evil  is  the  greatest  " nuisance"  in  the  world.  This 
is  a  broad  statement,  but  the  figures  are  available  to  prove  it. 
Other  nuisances  may  be  more  intensely  charged  with  evil,  but 
they  are  usually  confined  to  narrow  localities  and  affect  com- 
paratively few  people.  The  smoke  evil,  by  reason  of  its  wide- 
spread prevalence,  the  millions  that  come  under  its  influence  and 
the  hygienic  as  well  as  economical  considerations  involved,  easily 
ranks  as  the  chief  of  all  nuisances.  The  ''chimney  evil,"  would 
be  a  more  all-embracing  term  for  the  nuisance,  for  the  chimney 
is  responsible  for  more  things  of  an  evil  character  than  are  em- 
braced in  the  word  "smoke,"  as  it  is  commonly  employed  and 
understood.  When  the  "chimney  evil"  is  better  understood, 
there  will  be  a  general  amendment  of  smoke  ordinances.  The 
smoke  inspector  will  then  be  required  to  determine  the  nature 
of  the  poisons  the  chimney  is  contributing  to  the  atmosphere. 
He  will  devote  to  flue-gas  analysis  the  time  that  he  now  spends 
at  his  roost  upon  the  top  of  some  high  building,  making  notes  of 
the  colors  that  display  themselves  about  the  tops  of  neighboring 
chimneys.  When  the  flue  gases  are  right,  in  their  nature  and 
proportions,  there  will  be  no  smoke  to  offend  the  esthetic  tastes 
of  anybody.  Such  smoke  as  is  obnoxious  to  the  ordinances 
may  be  absent,  and  yet  there  may  exist  such  an  output  of  poison- 
ous gases  as  to  impair  the  health  of  everybody.  What  are  the 
real  evils  in  connection  with  the  smoking  chimney?  There  is 
so  much  misapprehension  upon  this  subject,  that  a  careful  in- 
quiry into  the  various  aspects  of  the  nuisance  is  apropos  and 
timely. 

The  "chimney  evil"  must  be  considered  from  two  stand- 
points: first,  a  hygienic  point  of  view,  the  public  health  taken 
into  account;  second,  an  economical  point  of  view,  damage  to 
and  waste  of  property  being  in  mind.  Our  inquiries  from  the 

41 


42  COMBUSTION  AND  SMOKELESS   FURNACES 

second  standpoint  should  follow  two  distinct  avenues,  (a)  damage 
to  public  and  private  property,  and  (6)  wastes  in  the  plant  with 
which  the  chimney  is  connected,  due  to  incomplete  combustion. 

As  health  is  a  matter  of  greater  moment  than  mere  dollars, 
the  hygienic  point  of  view  is  the  one  more  directly  concerning 
the  public.  The  chimney  evil  is  a  menace  to  health,  but  the 
greatest  dangers  lie,  not  so  much  in  the  black  and  unsightly 
element  commonly  called  smoke  as  in  the  noxious  gases  and 
vapors  that  accompany  black  smoke  and  are  sometimes  emitted 
from  the  stack  in  the  entire  absence  of  visible  smoke.  These 
gases  and  vapors  have  already  had  some  attention,  but  we  will 
look  into  them  a  little  further. 

Over  one  third  of  the  fuel  elements  of  soft  coal,  on  the  average, 
consist  of  volatile  matter,  and  may,  if  conditions  are  extremely 
bad,  be  given  off  through  the  stack.  From  500  to  700  Ib.  of  the 
constituents  of  one  ton  of  coal  may,  accordingly,  in  aggravated 
cases,  be  discharged  into  the  atmosphere.  To  this  must  be  added 
such  combustible  carbon  monoxide  gas  as  is  given  off  from  the 
coke  after  the  volatile  element  is  distilled.  These  figures  are  of 
course  far  above  the  average;  they  are  cited  only  as  indicative 
of  the  extent  of  evil  of  which  the  chimney  is  capable.  What 
proportion  of  this  tremendous  possible  output  concerns  the  anti- 
smoke  ordinance?  In  other  words,  what  proportion  of  the  dis- 
charge from  the  chimney  is  in  visible  form  as  floating  carbon, 
and  offensive  from  the  standpoint  of  the  smoke  inspector?  Under 
no  possible  circumstances  more  than  2  per  cent,  of  the  chimney 
discharge,  or  1  per  cent,  of  the  weight  of  the  coal.  The  average 
will  be  far  less  than  these  figures.  A  very  small  amount  of  soot, 
by  weight,  is  sufficient  to  give  color  to  a  very  large  volume  of  gas. 
What  shall  be  said  of  the  other  98  per  cent,  of  the  chimney  out- 
put? Has  the  public  no  concern  with  it  because  it  is  invisible? 
No  such  argument  would  be  raised  in  favor  of  immunity  for  the 
small-pox  microbe. 

Is  there  anything  inimical  to  health  in  soot?  It  may  tend 
to  clog  our  nostrils,  and  to  some  extent  to  block  the  air  passages 
of  the  lungs.  It  may  tend  to  shut  out  the  sun,  and  rob  us  of 
sunlight,  which  is  more  or  less  necessary  to  health.  This  is  about 
the  extent  of  the  evil  that  the  smoke  inspector  is  fighting,  so  far 
as  public  health  is  concerned.  Carbon  is  inert,  non-poisonous, 
and  is  not  destructive  of  the  tissues.  Coal  mining,  barring  the 


THE  CHIMNEY  EVIL  43 

physical  dangers  attending  it,  is  a  healthful  occupation  and  the 
coal  miner  is  usually  long-lived.  Postmortem  examinations 
have  developed  the  fact  that  the  lungs  of  the  coal  miner  may 
be  absolutely  black  with  the  coal  dust  inhaled  for  years,  and 
these  organs  be  otherwise  in  a  sound  and  normal  condition. 

Whatever  may  be  said  of  the  free  carbon  floating  in  the  gases, 
the  gases  themselves  are  not  entitled  to  any  claims  of  innocence. 
Let  us  see  how  powerful  the  gas,  carbon  monoxide,  is  as  a  health 
and  life  destroying  agent.  This  gas  is  one  of  the  chief  constit- 
uents of  "water  gas,"  the  commercial  gas  supplied  in  most  cases 
for  lighting  and  cooking  purposes,  and  we  know  the  result  of 
inhaling  fuel  gas  to  any  extent.  An  atmosphere  impregnated 
with  carbon  monoxide  to  the  extent  of  one  one-hundredth  of  one 
per  cent.,  if  breathed  for  a  sufficient  length  of  time  will  cause 
death.  If  the  air  is  impregnated  to  the  extent  of  5  per  cent., 
the  result  is  speedy  asphyxiation.  It  is  claimed  by  high  medical 
and  chemical  authorities  that  the  deadly  effects  of  carbon  mo- 
noxide are  greatly  increased  when  this  gas  is  mixed  with  carbon 
dioxide,  or  carbonic  acid  gas.  One  half  of  one  per  cent,  carbon 
monoxide,  in  company  with  5  per  cent,  carbonic  acid,  when  in- 
haled, is  as  quickly  destructive  of  life  as  5  per  cent,  of  carbon 
monoxide.  When  inhaled,  carbon  monoxide  causes  certain 
active  chemical  changes  in  the  blood,  directly  affecting  the  heart 
and  brain.  The  fact  that  this  gas  is  colorless  and  odorless,  and 
we  are  therefore  unable  to  detect  its  presence,  renders  it  all  the 
more  insidious.  It  is  fortunate  for  the  dwellers  in  large  cities 
that  carbon  monoxide  is  of  less  specific  gravity  than  air;  not- 
withstanding its  lighter  gravity,  we  get  more  of  it  than  is  good 
for  us,  the  amount  we  are  forced  to  breathe  depending  somewhat 
upon  atmospheric  conditions.  If  smoke  fresh  from  the  stack 
is  inhaled,  the  lungs  are  compelled  to  entertain  this  poisonous 
element  in  some  quantity.  No  chimney  should  be  tolerated, 
the  fresh  smoke  from  which  is  able,  under  any  circumstances,  to 
enter  the  windows  of  any  occupied  building.  The  mere  fact 
that  the  result  of  breathing  smoke-laden  air  is  not  immediately 
fatal  is  no  argument  for  the  toleration  of  the  evil.  The  cumu- 
lative effects  of  poison  taken  for  a  long  time  in  small  quantities 
may  be  entirely  disastrous  in  the  end. 

We  have  already  noticed  that  the  absence  of  black  smoke 
cannot  be  taken  as  proof  of  the  absence  of  poisonous  combustible 


44  COMBUSTION  AND  SMOKELESS  FURNACES 

gases.  This  is  a  fact  of  such  supreme  importance  in  connection 
with  the  chimney  question  that  it  will  bear  repetition.  Let  us 
see  under  what  circumstances  combustion  may  be  incomplete 
in  the  absence  of  offensive  smoke. 

A  change  in  method  of  firing  might  result  in  an  apparent 
change  in  volume  of  smoke  emitted,  while  the  actual  volume 
might  not  be  in  the  least  diminished.  Suppose,  for  instance,  a 
furnace  is  fired  every  20  minutes,  and  eight  scoops  of  coal,  four 
to  each  fire-door,  placed  in  the  furnace  at  each  firing.  If  condi- 
tions as  to  temperature  and  air  above  the  fire  should  be  bad,  a 
dense  volume  of  black  smoke  would  result  after  each  such  firing^ 
which  might  continue  for  six  or  seven  minutes,  gradually  dimin- 
ishing in  intensity  until  the  stack  would  clear  of  visible  smoke, 
at  which  condition  it  would  remain  until  the  next  firing.  The 
smoke  inspector  is  shocked  and  registers  his  protest.  The 
engineer  then  changes  the  method  of  firing,  and  two  scoops  of 
coal,  one  to  each  fire-door,  are  placed  in  the  furnace  at  intervals 
of  five  minutes.  It  is  evident  that  the  smoke  resulting  from  two 
scoops  of  coal  will  be  less  in  volume  and  density  than  that  from 
four  times  the  quantity.  If  conditions  are  such  that  better 
combustion  should  not  result  from  lighter  firing,  it  must  follow 
that  the  chimney  would  be  putting  forth  every  20  minutes  the 
same  volume,  both  of  gas  and  free  carbon  (though  the  quantity 
at  any  given  moment  might  not  be  sufficient  to  constitute  a 
violation  of  the  smoke  ordinance),  that  was  emitted  during  20 
minutes  when  all  of  the  eight  scoops  of  coal  were  placed  in  the 
furnace  at  one  stoking.  It  makes  little  difference,  so  far  as  the 
actual  nuisance  is  concerned,  whether  the  discharge  of  a  given 
volume  of  smoke  is  limited  to  the  fraction  of  a  given  period  of 
time,  or  whether  it  is  distributed  in  a  continuous,  but  less  pro- 
nounced manner,  over  the  entire  period.  It  is  probable  that 
the  lighter  firing  would  to  some  extent  improve  combustion,  but 
not  necessarily  so.  Other  methods  of  firing  may  be  employed 
to  fool  the  public  and  the  smoke  inspector,  without  necessarily 
diminishing  the  smoke  nuisance  in  the  least  particular. 

" Smokeless  furnaces"  are  not  always  what  they  seem.  It 
is  possible  to  remove  the  free  carbon  or  soot  from  the  gases,  and 
show  a  clean  stack,  without  in  the  least  improving  combustion, 
—  in  fact,  it  is  even  possible  to  show  a  clean  chimney  by  the 
employment  of  means  which  have  a  reactive  effect  upon  com- 


THE  CHIMNEY  EVIL  45 

bustion,  and  result  in  greatly  increasing  the  output  of  poisonous 
gases.  This  statement  appears  absurd  upon  the  face  of  it,  but 
it  is  one  of  the  many  well  proved,  if  strange,  facts  developed  by 
a  close  study  of  combustion.  The  author  may  perhaps  do  well 
to  marshal  some  authorities  in  support  of  this  contention. 

L.  W.  Dimond,  in  his  admirable  work  upon  the  Chemistry  of 
Combustion,  refers  to  this  matter.  He  speaks  of  certain  classes 
of  " smokeless  furnaces,"  which  employ  the  expedient  of  passing 
the  gases  over  highly  heated  surfaces  of  metal  or  tile,  and  makes 
the  following  observations: 

"When  from  an  insufficient  or  redundant  supply  of  air,  or 
from  other  causes,  combustion  is  incomplete,  the  carbonaceous 
constituent  of  the  coal  is  set  free  in  the  form  of  smoke.  This 
smoke  is  made  to  pass  over  heated  bars  of  iron,  or  other  heated 
substances,  and,  as  we  are  gravely  told,  is  'consumed.'  Car- 
bonic acid  is  always  mingled  with  the  smoke,  and  when  the  two 
are  brought  together  at  a  high  temperature,  as  by  contact  with 
the  heated  substances,  the  invisible  carbonic  acid  and  the  visible 
smoke  unite  (in  the  manner  before  described)  and  produce  in- 
visible carbonic  oxide.  This  we  are  asked  to  believe  is  'burning 
smoke';  but  in  truth,  the  form  only  is  changed  without  saving 
the  least  fraction  of  heat." 

This  author  might  also  have  added  with  perfect  truth  that 
there  is  an  actual  loss  of  heat  when  such  operation  occurs.  Ber- 
thollet's  Second  Law,  which  we  have  already  noted,  applies  in 
such  a  case.  We  have  shown  how  carbonic  acid  gas  may  be 
reconverted  by  a  reactive  operation  to  carbon  monoxide,  when 
free  carbon  is  encountered  in  the  absence  of  sufficient  oxygen. 
Such  free  carbon  is  present  in  smoke,  —  it  is  what  gives  smoke 
its  color.  It  is  accordingly  true,  as  pointed  out  by  Dimond,  that 
when  carbonic  acid  gas  and  smoke  encounter  each  other  in  the 
presence  of  temperature  and  the  absence  of  oxygen,  there  is  a 
union  resulting  in  carbon  monoxide,  and  a  disappearance  of  visible 
smoke.  Such  reactive  operation  is  attended  by  the  absorption 
or  disappearance  of  heat. 

It  is  necessary  at  this  stage  of  our  argument  to  advert  to 
" steam  jets"  to  some  extent,  while  leaving  a  more  extended 
discussion  of  these  devices  until  later. 

A  "  steam  jet,"  properly  installed  and  operated,  will  usually 
diminish,  if  not  entirely  suppress,  black  smoke  and  satisfy  the 


46 


COMBUSTION  AND  SMOKELESS   FURNACES 


smoke  inspector;  but  what  are  the  results  where  a  " steam  jet" 
is  employed,  with  respect  to  combustion  and  the  character  of 
the  chimney  gases?  Eckley  B.  Coxe,  in  the  Transactions  of  the 
New  England  Cotton  Manufacturers  Association,  session  of  1895, 
tells  of  tests  made  to  determine  the  relative  efficiency  of  mechan- 
ical draft  with  fan  blower  and  a  "steam  jet  smoke  consumer" 
device.  The  appearance  of  the  smoke  issuing  from  the  chimney 
was  not  relied  upon  as  necessarily  indicative  of  the  state  of  com- 
bustion. Flue  gas  analysis  was  employed  and  the  results  were 
extremely  illuminating  as  to  the  "steam  jet."  The  following 
table  shows  the  results  of  the  analysis: 


PER  CENT. 
OXYGEN 

PER  CENT. 
CARBON 
MONOXIDE 

PER  CENT. 
CARBON 
DIOXIDE 

PER  CENT. 
HYDROGEN 

PER  CENT. 
MARSH  GAS 

Fan  Blower. 
Steam  Jet.  .  . 

1.20 
0.30 

0.40 
13.15 

16.80 
8.20 

11.08 

2.00 

Note  the  tremendous  increase  of  carbon  monoxide,  the  poi- 
sonous product  of  incomplete  combustion;  the  decrease  of  carbon 
dioxide,  the  product  and  evidence  of  complete  combustion; 
and  the  presence  of  the  highly  combustible  marsh  gas,  —  all 
resulting  from  the  employment  of  the  "steam  jet."  There  was 
also  a  large  percentage  of  hydrogen,  resulting  from  the  dissocia- 
tion of  the  hydrogen  and  oxygen  contained  in  the  steam.  The 
presence  of  this  hydrogen  among  the  gases  is  indicative  of  a  great 
waste  of  heat,  as  the  dissociation  of  the  hydrogen  and  oxygen 
contained  in  one  pound  of  steam  represents  the  conversion  and 
disappearance  of  substantially  62,000  British  thermal  units, 
equal  to  the  energy  contained  in  about  four  and  one  half  pounds 
of  pure  carbon.  Is  it  possible  to  present  stronger  arguments  in 
favor  of  the  abandonment  of  stack  observations  by  the  smoke 
inspector  and  the  adoption  of  flue  gas  analysis  instead?  The 
smoke  inspector  of  course  has  no  concern  with  furnace  or  boiler 
efficiency,  but  he  should  be  directly  concerned  with  the  character 
of  the  gases  the  chimney  discharges  into  the  atmosphere  to  be 
breathed  by  the  tax  payer.  The  public  and  coal  consumer  should 
be  upon  their  guard  against  all  devices  which  apparently  improve 
combustion,  but  as  a  matter  of  actuality  retard  it  and  multiply 
the  output  of  poisonous  elements. 


THE  CHIMNEY  EVIL  47 

Other  poisonous  elements  are  discharged  by  the  chimney, 
but  they  do  not  possess  anything  approaching  the  virulent  prop- 
erties of  carbon  monoxide.  Bituminous  coal  usually  contains 
a  percentage  of  sulphur.  This  is  what  gives  soft  coal  smoke  its 
pungent  odor.  When  combustion  is  complete,  we  find  the  prod- 
uct (SO2),  sulphur  dioxide,  in  the  chimney  gases.  If  water  vapor 
is  present  to  any  extent,  we  are  likely  to  find  the  vapors  of  sul- 
phurous acid,  (H2SO3),  or  sulphuric  acid,  (H2S04).  The  gas, 
sulphur  dioxide,  would  be  to  a  great  extent  dissipated  in  the 
air,  but  the  acid  vapors  will  invariably  impregnate  the  soot,  as 
well  as  descend  of  their  own  gravity.  Surplus  moisture  in  the 
gases  tends  to  increase  the  output  of  acid  vapors,  and  in  this  we 
have  another  argument  against  the  use  of  the  " steam  jet."  Coal 
itself  contains  more  or  less  moisture,  and  a  certain  amount  of 
sulphurous  and  sulphuric  acid  vapors  are  inevitable,  but  there 
can  be  no  justification  for  such  an  increase  of  the  evil  as  follows 
the  use  of  the  ''steam  jet."  * 

We  have  been  furnished  with  pretty  accurate  data  as  to  the 
extent  in  which  we  may  expect  to  find  these  acid  elements  present 
in  ordinary  coal  smoke,  and  in  soot  deposits.  Dr.  R.  Angus 
Smith,  an  English  authority,  tells  us  that  .92  of  a  grain  will  be 
found  in  one  cubic  foot  of  smoke,  if  the  coal  contains  as  much  as 
1  per  cent,  sulphur. 

Some  very  exhaustive  experiments  were  made  at  Manchester, 
England,  in  1891,  to  determine  the  extent  of  soot  deposits  and 
the  proportion  of  sulphuric  acid  contained  therein.  Holly  leaves 
were  collected  and  the  deposits  which  they  carried  analyzed. 
The  figures  given  in  the  table  below  are  in  milligrams  of  deposit 


SAMPLE   TAKEN  AT 

SOOT 

(H2S04) 

Alexandra  Park 

131 

72 

Owens  College 

315 

10.4 

Hulme                                                                          

420 

26. 

Harpurhey                                     

443 

19. 

Infirmary.         

728 

27.5 

Albert  Square  

833 

24.2 

for  each  square  meter  of  surface.  The  first  samples  were  taken 
at  Alexandra  Park,  a  suburb,  and  succeeding  samples  taken  at 
intermediate  places  between  Alexandra  Park  and  Albert  Square, 
at  about  the  center  of  the  city.  The  table  shows  a  rapid  increase 


48  COMBUSTION  AND  SMOKELESS   FURNACES 

of  soot  deposits  as  the  center  of  the  city  was  approached,  and 
forms  a  good  argument  in  favor  of  life  in  the  suburbs  as  opposed 
to  residence  where  smoke  is  more  prevalent. 

If  the  tongue  is  touched  to  a  soot-covered  surface,  the  presence 
of  sulphuric  acid  will  be  indicated  by  a  sour  taste  in  the  mouth. 

Dr.  Cohen,  of  Leeds,  England,  a  number  of  years  ago  devoted 
a  great  deal  of  painstaking  investigation  to  the  subject  of  the 
atmosphere  of  cities.  Some  of  his  conclusions  are  interesting. 
He  estimated  that  fully  20  tons  of  soot  descended  upon  the  city 
of  Leeds  every  24  hours.  He  found  the  soot  to  be  loaded  with 
ammonium  sulphate  and  free  sulphuric  acid.  He  charges  the 
vicious  character  of  the  fogs  that  at  times  prevail  in  great  cities, 
notably  in  London,  to  the  presence  of  soot  and  sulphuric  acid. 
These  fogs  when  breathed  are  accompanied  by  considerable 
irritation  of  the  lungs  and  air  passages.  As  to  the  presence  of 
carbonic  acid  gas,  Dr.  Cohen  says  that  the  air  of  the  large  city 
contains  one  third  more  of  this  element  than  the  air  of  the  coun- 
try. While  carbonic  acid  gas  is  not  poisonous  to  any  extent, 
its  presence  in  increased  quantities  means  the  displacement  of  a 
certain  quantity  of  life-giving  oxygen,  while  the  lungs  require  all 
of  the  oxygen  found  in  the  natural  state  of  the  air. 

There  is  certainly  a  marked  difference  between  the  atmos- 
phere of  the  country  and  that  of  the  city.  The  difference  may 
be  readily  detected  by  the  senses.  The  odds  are  in  favor  of 
country  air,  as  there  is  no  doubt  that  a  smoke-laden  atmosphere 
tends  to  an  increase  in  mortality,  especially  with  diseases  affecting 
the  nose,  throat,  and  pulmonary  organs. 

It  is  impossible  to  estimate  the  damage  resulting  to  health 
and  property  from  the  " chimney  evil"  in  a  city  like  Chicago, 
for  instance,  with  an  annual  consumption  of  soft  coal  running 
far  into  the  millions  of  tons.  If  any  one  doubts  the  extent  of 
the  Chicago  smoke  nuisance,  let  him  ascend  to  the  roof  of  one 
of  the  high  buildings  in  the  down-town  district  and  look  out  upon 
the  sea  of  erupting  chimneys.  The  prospect  will  be  suggestive 
of  the  inferno.  "Looks  like  hell  with  the  lid  off,"  was  the  laconic 
observation  of  a  visitor,  coming  from  a  locality  where  unadul- 
terated air  and  sunshine  are  the  heritage  of  everybody.  He  had 
expected,  on  ascending  to  the  roof  of  the  sky-scraper,  that  a 
panorama  would  unfold  itself  in  every  direction,  extending  to 
the  city  limits.  A  bowshot  was  about  the  extent  of  his  vision. 


THE  CHIMNEY  EVIL  49 

A  passenger  upon  a  steamer  approaching  Chicago  will,  if  the 
wind  is  right  and  atmospheric  conditions  favorable,  be  treated 
to  a  spectacular  exhibition  of  the  smoke  nuisance  that  curses  the 
city.  The  steamer  will  pass  from  an  atmosphere  of  pure  air  and 
bright  sunlight  into  a  smoke  bank  so  dense  as  to  make  the  con- 
stant use  of  the  steam  siren  necessary  to  avoid  collision  with 
other  vessels. 

That  the  dense  and  constant  baptism  of  smoke  afflicting 
Chicago  and  other  large  cities,  leads  to  immense  property  loss 
cannot  be  disputed.  It  is  idle  to  attempt  to  compute  this  loss, 
with  anything  like  accuracy.  One  statistician  with  a  gift  for  fig- 
ures places  the  annual  damage  in  Chicago  at  forty  million  dollars. 
Another,  more  conservative,  places  the  annual  loss  at  twelve 
million  dollars.  To  police  the  city  against  this  foe  to  health 
and  despoiler  of  property,  Chicago  provides  four  smoke  inspectors. 

The  damages  wrought  by  the  smoke  nuisance  are,  or  ought 
to  be,  so  well  understood  that  it  seems  superfluous  to  dilate  upon 
them.  They  have  been  recognized  ever  since  soft  coal  first  made 
its  appearance  as  an  article  of  fuel.  One  Evelyn,  in  a  pamphlet 
entitled  "  Fumif ugina,"  published  in  the  reign  of  Charles  the 
First,  attacked  the  nuisance  as  follows: 

"It  is  this  horrid  smoke,  which  obscures  our  churches  and 
makes  our  palaces  look  old,  which  fouls  our  clothes  and  corrupts 
the  waters,  so  that  the  very  rain  and  refreshing  dews  which  fall 
in  the  several  seasons  precipitate  this  impure  vapor,  which,  with 
its  black  and  tenacious  quality,  spots  and  contaminates  whatever 
is  exposed  to  it. 

"It  is  this  which  scatters  and  strews  about  these  black  and 
smutty  atoms  upon  all  things  where  it  comes,  —  insinuating 
itself  into  our  very  secret  cabinets  and  most  precious  repositories. 
Finally,  it  is  this  which  diffuses  and  spreads  a  yellowness  upon 
our  choicest  pictures  and  hangings;  which  is  like  Avernus  to 
fowls  and  kills  our  bees  and  flowers  abroad,  suffering  nothing 
in  our  gardens  to  bud,  display  itself  or  ripen,  so  that  our  anemones 
and  many  other  choicest  flowers  will  by  no  industry  be  made  to 
bloom  in  London  or  the  precincts  of  it,  unless  they  be  raised  in 
a  hot-bed  and  governed  with  extraordinary  artifice  to  accelerate 
their  springing,  imparting  a  bitter  and  ungrateful  taste  to  those 
few  wretched  fruits,  which,  never  arriving  at  their  desired  ma- 
turity, seem,  like  the  apples  of  Sodom,  to  fall  even  to  dust  when 
they  are  but  touched." 

Evelyn  employed  rather  strong  language,  but  he  set  forth 
AUTHOR'S  NOTE:   Since  this  book  was  written,  in  1906,  Chi- 
cago has  taken  a  position  at  the  head  of  all  cities  in  the  war 
against  smoke.    The  city  now  has  what  is  probably  the  best  or- 
ganized smoke  inspection  department  in  the  world. 


50  COMBUSTION  AND  SMOKELESS   FURNACES 

the  situation  in  something  like  its  real  colors.  There  are  local- 
ities in  Chicago,  and  doubtless  in  many  large  cities,  where  vegeta- 
tion refuses  to  grow,  on  account  of  the  poisons  with  which  the 
atmosphere  is  laden.  And  in  such  an  atmosphere  of  filth  and 
poison,  little  children  are  born  and  reared,  if  they  are  so  fortunate 
as  to  live,  deprived  of  the  pure  air  and  sunshine  that  nature  has 
provided  for  them. 

The  London  Lancet  asserts  that  the  injuries  inflicted  by  smoke 
on  the  health  of  the  people  of  London  are  of  greater  consequence 
than  the  property  damage. 

An  anti-smoke  conference  was  recently  held  in  London,  and 
many  interesting  facts  were  brought  out  in  the  discussions;  some 
of  these  facts  are  worth  citing: 

Upwards  of  a  million  tons  of  matter,  heavily  impregnated 
with  sulphuric  acid,  are  annually  ejected  into  the  atmosphere 
of  London.  Metals  are  corroded  and  statuary  injured  almost 
beyond  redemption  by  the  sulphuric  vapors.  Tapestries,  fres- 
coes, paintings,  and  other  works  of  art  are  injured,  and  in  many 
cases  utterly  ruined,  by  the  soot  and  acid  vapors,  which  pene- 
trate everywhere.  The  employment  of  light  colored  building 
materials  means  a  superfluous  effort  and  expense.  No  building 
relying  upon  such  features  for  its  beauty  can  expect  to  retain 
them.  Its  face  is  daubed  with  the  dun  hue  of  London  before 
the  walls  are  completed. 

Plants  are  killed  by  the  soot  deposits  and  the  effects  of  the 
acids  contained  in  them.  Even  when  washed  frequently  they 
cannot  attain  to  anything  like  their  normal  luxuriance. 

It  was  estimated  that  upwards  of  one  half  of  the  sunlight  is 
shut  off  from  London  by  the  great  clouds  of  smoke  and  vapor 
that  overspread  the  city  like  a  vast  umbrella. 

Yet  we  are  told  that  London  has  made  great  strides  in  the 
direction  of  smoke  abatement  as  compared  with  American  cities. 
No  doubt  London  is  in  advance  of  many  other  municipalities  in 
this  particular. 

It  seems  strange,  when  we  consider  how  early  the  smoke 
nuisance  came  into  prominence  as  a  vital  public  question,  that 
so  little  progress  has  been  made  in  the  campaigns  against  it. 
This  may  be  accounted  for,  perhaps,  by  the  tremendous  demands 
for  power  to  operate  the  machinery  of  this  mechanical  age. 

Soft  coal  smoke  was  first  recognized  as  an  evil  in  England 


THE  CHIMNEY  EVIL  51 

over  six  hundred  years  ago.  The  first  smoke  ordinance  was  far 
more  stringent  than  any  of  its  successors.  During  the  reign  of 
the  first  Edward,  a  statute  was  passed,  making  the  consumption 
of  "sea  coal"  a  capital  offense,  the  theory  being  that  one  good 
hanging  would  avail  more  with  the  offender  than  any  number 
of  fines.  There  was  further  agitation  of  the  subject  during  the 
reign  of  Elizabeth.  A  proclamation  was  issued,  making  the 
burning  of  " stone  coal"  during  the  sitting  of  parliament  an 
offense,  as  it  was  believed  the  smoke  was  injurious  to  the  health 
of  the  Knights  of  the  Shire.  It  was  not,  however,  until  1785  that 
any  sensible  and  concerted  steps  were  taken  in  England  in  the 
direction  of  smoke  abatement.  A  great  deal  was  accomplished 
in  London,  Manchester,  Leeds,  and  other  cities  in  Great  Britain, 
during  the  latter  half  of  the  last  century,  and  the  Englishman  of 
to-day  considers  smoke  abatement  as  one  of  the  leading  public 
questions. 

More  has  been  accomplished  in  Germany  and  France  than  in 
England.  In  Berlin  the  fireman  is  given  a  course  of  instruction 
under  the  supervision  of  the  government,  and  great  good  results, 
both  to  the  public  through  the  decrease  of  smoke  and  to  the  con- 
sumer through  the  improvement  in  combustion.  Paris  insists 
upon  the  use  of  coke  and  other  smokeless  fuels  as  far  as  possible. 

American  cities  contiguous  to  the  anthracite  coal  fields  are 
improving  their  atmospheres  by  the  use  of  hard  coal.  The  gen- 
eral use  of  such  a  fuel  is,  however,  prohibitive  for  power  purposes 
in  most  cities,  owing  to  the  cost.  Anthracite,  moreover,  is  not  as 
well  adapted  for  power  as  the  bituminous  coals.  The  city  en- 
joying its  general  employment  should  not  congratulate  itself  too 
freely  on  immunity  from  the  "chimney  evil,"  as  large  possibil- 
ities of  danger  are  involved  in  the  poisonous  oxides  that  accom- 
pany its  combustion. 

Great  as  are  the  property  losses  inflicted  upon  the  public  by 
the  "chimney  evil,"  it  is  probable  that  financial  losses  almost 
as  great  are  sustained  by  the  owners  of  plants  responsible  for 
the  smoke.  The  fuel  losses  arising  from  incomplete  combustion 
have  already  to  some  extent  been  noticed.  When  we  consider 
the  coal  consumption  of  Chicago,  the  losses  which  the  smoking 
chimneys  inflict  upon  their  owners  total  in  their  probabilities 
up  into  appalling  figures.  The  following  statistics  are  considered 
reliable  for  1905: 


52  COMBUSTION   AND  SMOKELESS   FURNACES 

CHICAGO  COAL  RECEIPTS 


Anthracite,  by  rail 

Anthracite,  by  lake 

Pennsylvania,  Bituminous 

Ohio,  Bituminous 

West  Virginia,  Bituminous 

Indiana,  Bituminous 

Illinois,  Bituminous 

Coke.. 


Tetal. 


808,158 

942,720 

663,648 

594,851 

933,117 

2,672,138 

4,012,752 

463,710 


11,091,094 


CHICAGO  COAL  SHIPMENTS 


577,439 

2,095,671 

292,204 


Anthracite 

Bituminous 

Coke 

Total 2,965,314 

Chicago  Coal  Consumption 8,126,780 

The  value  of  the  coal  consumed  in  Chicago  in  1905  is  esti- 
mated at  $32,513,000.  Taking  the  smallest  percentage  of  prob- 
able loss,  by  reason  of  incomplete  combustion,  and  applying  it 
to  these  figures,  we  get  a  result  in  dollars  wasted  that  will  shock 
the  economist. 

We  have  noticed  to  some  extent  the  difficulties  that  the  steam 
boiler  offers  to  the  consummation  of  combustion.  We  will  now 
devote  ourselves  to  an  inquiry  into  the  means  that,  may  be  em- 
ployed to  overcome  these  difficulties  and  minimize  the  losses 
sustained  by  the  coal  consumer. 

Boiler-room  economies  have  been  largely  neglected  by  the 
owner  of  the  power  plant,  who  has  been  exceedingly  industrious 
in  his  search  elsewhere  for  the  economies,  big  and  little.  Prac- 
tices are  commonly  permitted  here,  which,  if  duplicated  in  other 
departments,  would  soon  put  the  concern  owning  the  plant  into 
bankruptcy.  Why  is  it  that  the  manufacturer  will  pay  fabulous 
prices  for  machinery  designed  to  reduce  the  cost  of  manufacturing 
an  article  the  fraction  of  a  per  cent.,  and  permit,  without  thought, 
fuel  and  other  wastes  to  occur  in  the  boiler  room,  which,  if  ar- 
rested, would  reduce  the  manufacturing  cost  of  the  same  article 
many  times  that  fraction?  The  question  will  be  left  for  some 
one  else  to  answer.  Our  business  is  to  show  how  these  wastes, 
which  we  believe  will  be  generally  conceded,  may  be  arrested 
and  turned  into  profits. 


THE  CHIMNEY  EVIL  53 

The  wastes  that  occur  in  the  boiler  room  are  chargeable  to 
three  sources: 

1st.  Improper  equipment  and  installation.  The  architect 
designing  the  boiler  room  and  surroundings,  and  the  engineer 
designing  the  plant  and  specifying  the  equipment,  are  responsi- 
ble. 

2d.  Improper  and  unintelligent  handling  of  the  furnace, 
the  boiler  and  its  accessories.  The  fireman  and  engineer  are 
responsible. 

3d.  The  use  of  a  fuel  that  will  not  yield  the  maximum  of 
heat  energy  at  the  minimum  of  cost.  The  purchasing  agent,  or 
whoever  is  charged  with  buying  the  coal  and  seeing  that  the 
article  bought  is  delivered,  is  responsible. 

With  the  first  source  of  waste  we  cannot  deal  to  any  extent, 
as  it  involves  too  wide  a  discussion  of  engineering  subjects.  We 
will  only  say  that  crimes  against  good  engineering  are  too  com- 
monly committed  by  the  architect  and  designing  engineer.  The 
men  in  the  boiler  room  must  not  be  expected  to  carry  on,  with 
a  high  degree  of  efficiency,  the  nice  chemical  processes  necessary 
to  release  the  heat  energy  stored  in  the  coal  and  convey  it  to 
the  cylinder  of  the  engine,  if  provided  with  equipment  or  tools, 
so  inefficient  or  unsuitable  as  to  render  good  results  impossible. 
If  the  boiler  plant  and  accessories  are  everything  that  could  be 
reasonably  expected,  and  a  fuel  is  given  the  fireman,  rich  in  ash 
and  moisture  and  everything  else  except  heat  units,  the  best 
results  are  out  of  the  question.  A  fuel  should  be  selected  that 
is  adapted  to  the  grates,  draft,  and  general  conditions  under 
which  the  plant  is  operated.  Some  standard  should  be  adopted 
for  measuring  the  efficiency  of  the  coal,  —  the  net  cost,  for  in- 
stance, of  evaporating  a  thousand  pounds  of  feed  water.  Trial 
runs  on  various  grades  of  fuel  will  develop  many  facts  as  to 
availability  of  coal,  and  lead  to  the  selection  of  a  fuel  best 
designed  for  the  plant. 

Assuming  that  the  fireman  is  provided  with  the  fuel  best 
adapted  to  the  furnace  and  boiler,  let  us  look  at  the  second  source 
of  loss,  and  see  what  steps  can  be  taken  to  secure  increased  effi- 
ciency. In  this  case,  the  fireman  is  primarily  the  responsible 
party.  The  engineer  is  secondarily  responsible,  as  it  is  a  part 
of  his  business  to  see  that  correct  practices  obtain  in  the  boiler 
room.  Too  low  an  estimate  is  usually  placed  upon  the  qualifica- 


54  COMBUSTION  AND  SMOKELESS   FURNACES 

tions  necessary  to  produce  a  good  fireman.  To  handle  furnace 
and  boiler  properly  requires  expert  knowledge,  reinforced  by 
considerable  experience.  The  fireman  is  in  many  respects  the 
most  important  man  about  the  plant.  He  stands  at  the  very 
source  and  fountain  head  of  the  energy  necessary  to  the  plant, 
and  conserves  or  wastes  it.  A  premium  should,  and  soon  will 
be,  placed  upon  his  intelligence  and  efficiency.  The  Japanese 
government  recognizes  the  truth  of  these  statements.  It  pays 
as  much  attention  to  the  education  of  the  firemen  upon  its  battle- 
ships as  it  does  to  training  the  men  who  handle  the  great  rifles 
in  the  turrets.  The  man  behind  the  shovel  is  recognized  as 
standing  behind  the  man  behind  the  gun.  It  is  due  in  no  small 
measure  to  the  Japanese  firemen  that  the  efficiency  of  Togo's 
squadron  stands  as  a  model  for  the  navies  of  the  world. 

Now  let  us  see  what  qualifications  the  fireman  must  possess, 
in  order  to  satisfy  the  manager  of  the  average  steam  plant.  He 
must  have  sufficient  muscle  to  enable  him  to  shovel  any  required 
amount  of  coal.  He  must  be  sufficiently  alert  to  watch  the 
steam  *and  water  gages  and  see  that  they  register  properly, — 
that  sufficient  steam  goes  to  the  engine  and  that  the  boiler  does 
not  blow  Up.  How  he  produces  this  steam,  and  how  much  coal 
he  consumes  in  getting  it,  are  matters  that  he  is  left  to  work  out 
in  his  own  way.  Is  he  required  to  answer  any  questions  about 
combustion  and  how  to  attain  it  with  the  greatest  economy  in  a 
steam  boiler  furnace?  Is  he  expected  to  know  anything  about 
the  character  or  temperature  of  the  escaping  flue  gases,  —  what 
these  ought  to  be  and  how  to  secure  them?  Can  he  explain  the 
various  approved  methods  of  firing,  and  does  he  know  when  and 
how  to  employ  them?  In  Germany,  the  fireman  is  compelled 
to  know  something  about  these  things.  He  is  required  to  spend 
at  least  fifteen  days  under  a  government  instructor,  and  pass 
an  examination  before  he  is  given  charge  of  a  boiler.  The  German 
is  proverbially  thrifty  and  cannot  view  waste  in  the  boiler  room, 
or  elsewhere,  with  complacency.  When  the  owner  of  the  American 
power  plant  fully  awakes  to  the  fact  that  the  boiler  room  needs 
more  attention,  he  will  insist  upon  the  same  degree  of  efficiency 
and  intelligence  here  that  characterizes  the  typical  American 
power  and  manufacturing  plant  in  its  other  departments.  Proper 
handling  of  the  shovel  will  do  much  to  increase  efficiency,  and 
just  as  much  to  abate  the  "  chimney  evil,"  but  with  boilers  and 


THE  CHIMNEY  EVIL  55 

furnaces  as  we  have  them  the  highest  results  are  impossible, 
without  the  employment  of  some  accessory  to  boiler  or  furnace. 

An  extended  consideration  of  the  third  source  of  waste  noted 
would  be  outside  our  province,  —  it  will  be  left  with  the  few 
suggestions  already  offered  bearing  upon  it. 

Little  progress  can  be  made  with  combustion  studies  in  any 
power  plant  unless, apparatus  is  employed  to  measure  both  the 
completeness  and  the  efficiency  of  combustion.  Complete  com- 
bustion is  not  necessarily  complete  combustion.  Many  plants 
that  never  smoke  at  all  evaporate  less  water  per  pound  of  com- 
bustible than  other  plants  that  are  bad  smokers. 

Author's  Note: — For  a  discussion  of  combustion  testing 
apparatus,  see  Appendix. 


CHAPTER  V 

SMOKELESS  FURNACES  IN  GENERAL 

THERE  has  been  considerable  discussion  relative  to  the  use 
of  the  term  "  smoke-consuming  furnace/'  —  some  authorities 
maintaining  that  it  is  possible  to  " prevent"  smoke,  but  impos- 
sible to  burn  it.  Chas.  Wye  Williams,  who  was  the  inventor 
of  a  "  smokeless  furnace,"  and  who  wrote  a  book  to  advertise 
it,  seems  to  have  been  the  progenitor  of  the  idea  that  smoke, 
once  formed,  cannot  be  burned.  This  doctrine  has  been  preached 
to  a  great  extent  by  engineering  writers,  and  it  will  be  found  in 
the  literature  of  a  great  many  "  smokeless  furnaces."  William 
Kent,  in  his  "Steam  Boiler  Economy,"  says,  "Smoke  may  be 
burned,"  and  gives  his  reasons  for  this  view  of  the  matter  as 
follows : 

"This  last  statement  is  contrary  to  that  made  by  Chas.  Wye 
Williams  in  his  treatise  on  '  The  Combustion  of  Coal  and  the  Pre- 
vention of  Smoke/  first  printed  about  sixty  years  ago,  and  copied 
extensively  by  later  writers,  viz.,  that  'when  smoke  is  once  pro- 
duced in  a  furnace  or  flue,  it  is  as  impossible  to  burn  it  or  convert 
it  to  heating  purposes  as  it  would  be  to  convert  the  smoke  issuing 
from  the  flame  of  a  candle  to  the  purposes  of  heat  or  light/  The 
error  of  the  statement  made  by  Mr.  Williams  can  be  easily  shown 
by  a  simple  experiment  which  has  been  made  by  the  author.  A 
short  piece  of  candle  was  placed  inside  of  a  tall,  narrow  tin  cylin- 
der. The  deficient  supply  of  air  the  candle  thus  received  caused 
it  to  give  off  a  column  of  black  smoke.  This  was  caused  to  pass 
into  the  central  draft  tube  of  a  Rochester  kerosene  lamp,  and 
as  it  passed  up  into  the  flame  of  the  lamp  it  was  completely 
burned,  not  a  trace  of  smoke  being  visible  in  the  lamp  chimney. 
The  experiment  was  also  made  with  a  still  larger  column  of  smoke, 
produced  by  burning  paper  under  the  lamp  with  the  same 
result." 

No  less  an  authority  than  Professor  Hutton  of  Columbia 
University  takes  the  opposite  view  of  the  case,  as  follows: 

56 


SMOKELESS   FURNACES  IN  GENERAL  57 

"The  term  'smoke  combustion'  or  'smoke  burning/  is  an 
improper  one.  Lampblack  when  once  made  is  incombustible 
and  cannot  be  burned." 

Professor  Hutton  contents  himself  with  this  bare  statement 
of  alleged  fact,  and  gives  no  reasons  why  carbon  in  the  form  of 
lampblack  or  soot  is  not  combustible,  while  in  other  forms 
everybody  knows  it  is  highly  so.  The  writer  agrees  with  William 
Kent,  that  smoke  is  combustible,  and  that  carbon  in  this  form, 
given  the  right  conditions,  may  be  as  readily  burned  as  in  any 
other.  He  is  confirmed  in  this  opinion  by  the  following  experi- 
ment, which  is  recommended  to  any  one  possessed  of  doubts  as 
to  the  combustibility  of  soft  coal  smoke: 

If  a  small  quantity  of  coal,  crushed  to  about  the  fineness  of 
bird  shot,  is  placed  in  the  bowl  of  an  ordinary  clay  pipe,  the  bowl 
of  the  pipe  stopped  with  clay  or  otherwise  and  then  heated  to  a 
point  approaching  red  heat,  smoke  will  issue  from  the  stem  of 
the  pipe,  and  may  be  ignited,  when  it  will  burn  with  a  white 
flame  and  with  the  entire  absence  of  smoke.  The  flame  may  be 
blown  out,  and  smoke  will  again  issue.  It  will  have  the  color 
and  odor  of  the  volatile  coal  gases,  which  escape  from  the  chimney 
and  is  of  the  same  character,  with  the  exception  that  little  or  no 
carbonic  oxide  will  be  present,  owing  to  the  distillation  taking 
place  in  the  absence  of  air.  The  discharge  of  gas  and  smoke 
will  continue  from  the  pipe  stem  for  some  minutes,  and  when  it 
ceases,  the  coal  in  the  pipe  bowl  will  be  found  to  be  coked.  The 
process  in  the  pipe  bowl  is  quite  similar  to  that  which  occurs  in 
the  retorts  of  gas  works.  It  will  be  noticed  that  the  smoke  refuses 
to  ignite  until  the  pipe  bowl  approaches  the  point  of  red  heat. 
If  the  pipe  stem  is  heated  to  a  similar  degree,  the  smoke  will 
burn,  if  ignited,  the  moment  it  begins  to  issue.  Here  we  have 
another  proof  that  heat  is  an  important  element  in  the  combus- 
tion of  smoke. 

One  of  the  earliest  "  smoke-consuming "  devices  invented 
consisted  of  two  furnaces,  in  one  of  which  the  green  coal  was 
fired  and  the  gases  distilled  or  " sublimed."  The  smoke  and 
gases  were  then  conducted  from  this  furnace  to  a  point  beneath 
the  grates  of  a  second  furnace,  carrying  a  bed  of  incandescent 
fuel.  It  was  found  that  the  smoke,  in  passing  up  through  the 
fuel,  was  completely  consumed. 

Other  devices  were  patented  at  an  early  date  and  some  are 


58  COMBUSTION  AND  SMOKELESS   FURNACES 

on  the  market  to-day,  which  return  the  smoke  from  the  breeching 
or  smoke-box  of  the  boiler,  mixing  it  with  air  and  delivering  it 
to  the  ash-pit  of  the  furnace.  The  smoke,  in  such  case,  will 
burn  in  passing  through  the  incandescent  fuel  on  the  grates. 
The  writer  considers  it  to  be  a  well  established  fact  that  smoke, 
or  the  free  carbonaceous  element  floating  in  the  chimney  gases, 
is  combustible,  and  that  the  appellation  " smoke  consumer" 
is  not  a  misnomer.  Every  farmer's  boy  knows  that  soot  is  com- 
bustible, and  that  the  house  chimney  rids  itself  of  this  element 
by  " burning  out." 

Before  entering  upon  a  discussion  of  the  various  classes  of 
"  smokeless  furnaces/'  which  will  necessarily  involve  some 
criticisms,  the  author  desires  to  state  that  all  such  criticisms  are 
based  upon  the  well-understood  principles  of  combustion  already 
set  forth,  and  such  practical  facts  as  will  be  conceded  by  every 
well-informed  engineer;  the  aim  being  to  suggest  such  guides  as 
will  enable  any  one  to  select  from  the  hundreds  of  devices  upon 
the  market,  good,  bad,  and  indifferent,  that  one  which  will  be 
best  adapted  to  the  peculiar  conditions  obtaining  in  his  plant. 
In  the  neighborhood  of  fifteen  hundred  United  States  patents 
are  in  force  upon  furnaces  and  other  devices  to  promote  com- 
bustion. It  is  obvious  that  these  devices,  if  we  are  to  make  any 
pretense  of  covering  the  field,  must  be  dealt  with  in  groups  or 
classifications,  otherwise  the  task  would  be  endless.  A  supple- 
ment to  this  book  would  have  to  be  issued  with  every  appearance 
of  the  Patent  Office  Gazette.  The  number  of  changes  that  can 
be  rung  on  substantially  the  same  thing,  each  one  presenting  some 
small  feature  of  patentability,  is  truly  astonishing. 

What  are  the  requisites  of  a  good  ''smokeless  furnace"? 

1st.  It  must  prove  efficient  as  a  "smoke  consumer,"  no 
matter  what  grade  of  coal  is  used  or  what  method  of  firing  is 
employed. 

2d.  It  must  be  capable  of  adjustment,  by  test  arid  experi- 
ment, to  meet  all  conditions  of  draft,  coal  consumption,  etc., 
etc.,  —  presented  by  any  boiler,  as  no  code  of  specifications  can 
be  drawn  in  advance  to  exactly  meet  the  conditions  in  any  given 
case. 

3d.  It  must  prove  economical,  —  i.e.,  increase  efficiency 
and  reduce  coal  bills.  Improved  efficiency  should  accompany 
improved  combustion,  but  as  has  been  shown  this  is  not  neces- 
sarily the  case  with  a  smoke-consuming  furnace. 


SMOKELESS   FURNACES   IN   GENERAL  59 

4th.  It  must  act  automatically  and  thus  insure  the  very 
highest  economy,  without  requiring  constant  attention  and  hand- 
manipulation  by  the  fireman.  The  term,  "  automatically/'  is  used 
with  particular  reference  to  the  introduction  of  air  into  the  fire- 
box, at  such  times  and  in  such  manner  as  will  meet  the  changing 
conditions  as  to  combustible  gases. 

5th.  It  must  be  low  in  cost,  and  within  the  reach  of  the 
owner  of  the  small  plant. 

6th.  It  must  prove  durable  and  not  require  incessant  re- 
pairs, with  the  incidental  annoyance  and  expense  of  shutting 
down  the  plant  at  frequent  intervals  and  inconvenient  times. 

No  argument  should  be  necessary  to  establish  the  fact  that 
the  above  requisites  are  imperative.  The  necessity  of  air  regu- 
lation has  already  been  pointed  out  in  connection  with  the  dia- 
gram, Fig.  2,  which  illustrates  the  correct  method  of  supplying 
air  to  the  fire-box  of  a  hand-fired  boiler  furnace,  to  meet  the  con- 
ditions. Such  regulation  should  be  automatic  and  independent 
of  the  will  of  the  fireman,  otherwise  it  might  receive  little  atten- 
tion and  be  of  correspondingly  little  use.  The  imperative  neces- 
sity of  air  regulation  is  conceded  by  all  of  the  leading  engineering 
writers,  who  have  touched  at  all  upon  the  subject.  Many  of 
them  emphasize  the  fact  that  such  regulation  should  be  auto- 
matic. As  long  ago  as  1843,  the  English  engineer,  Houldsworth, 
settled  the  importance  of  air  regulation,  by  careful  and  exhaustive 
experiments.  In  these  experiments,  the  air  was  regulated  by 
"sight,"  which  will  answer  in  the  case  of  a  test,  but  would  be  out 
of  the  question  in  every-day  practice,  as  it  would  necessitate  the 
attendance  of  an  experienced  man  at  the  dampers.  Houlds- 
worth  assumed  the  efficiency  of  the  boiler,  all  air  excluded  from 
the  fire-box,  as  100.  He  found,  when  burning  Oldham  coal, 
with  constant  air  apertures  of  35  square  inches  leading  to  the 
fire-box,  that  the  efficiency  was  94,  and  that  when  the  air  was 
regulated  to  meet  the  changing  requirements  of  the  gases,  the 
efficiency  was  114.  With  Clifton  coal,  he  found  that  the  efficiency 
with  air  regulation  was  135. 

Excess  air,  strange  as  it  may  seem,  leads  to  an  increase  in 
stack  temperature,  —  the  surplus  air  more  readily  taking  on  the 
heat  of  the  gases,  through  which  it  is  passed,  than  the  heating 
plates  of  the  boiler  will  absorb  it.  M.  Burnat,  of  France,  gives 
the  following  results  illustrating  the  increase  of  stack  temperature 
as  the  excess  of  air  increases: 


60 


COMBUSTION   AND  SMOKELESS   FURNACES 


CUBIC   FEET   OF   AIR   AT  62°   FAHR. 
PER   LB.  OF   COAL 


AVERAGE   TEMPERATURE   OF   GASES 
LEAVING   BOILER   FLUES 


272 
196 
168 
124 


624 
601 
550 

487 


" Smokeless  furnaces"  may  be  variously  classified,  —  such 
division  being  largely  an  arbitrary  matter.  The  author  has,  for 
purposes  of  convenience,  adopted  the  following  classification: 


I.     Mechanically 
Fired  Furnaces 


1.  Underfeed  Stokers 


2.  Overfeed  Stokers 


(a)  Horizontal  Moving  Grates 
(&)  Inclined  Movable  Grates 

(c)  Fuel  Spreaders 

(d)  Pulverized  Fuel  Burners 


II. 


Hand-Fired 
Furnaces 


1.  Mechanical  Draft 


j(a)  Air  Blowers 

V 


2.  Natural  Draft 


(6)  Steam  Blowers 

(a)  Steam  Jet  Auxiliaries 

1.  Grate  Admission 

2.  Fire-door    Admis- 

sion 

3.  Side-wall     Admis- 
(6)  Air  Furnaces-j        sion 

4.  Bridge-wall  Ad- 

mission 

5.  Arch  Admission 

6.  Miscellaneous 

(c)  Fire-arch  Furnaces 

(d)  "  Dutch-oven  "  Furnaces 
(«)  "Down-draft"  Furnaces 


The  attention  of  the  reader  is  redirected  to  the  following 
facts,  which  are  vital,  and  must  be  borne  in  mind  when  consider- 
ing the  merits  of  any  device,  claiming  to  assist  combustion  and 
increase  boiler  or  furnace  efficiency: 

There  are  three  prime  requisites  to  the  combustion  of  the 
gases  discharged  in  the  fire-box:  1,  a  sufficient  supply  of  free 
air  in  the  fire-box  and  intermixed  with  the  gases;  2,  a  sufficient 
temperature  at  the  point  and  moment  of  ignition;  3,  suffi- 
cient room  for  the  expansion  of  the  burning  gases  during  the  act 
of  their  combustion. 

There  are  other  requisites,  secondarily  essential,  which  will 
be  noticed  as  the  discussion  proceeds. 


CHAPTER  VI 

MECHANICAL    STOKERS 

THE  mechanical  stoker  is  by  no  means  a  recent  invention, 
and  there  is  little  that  is  new,  except  mere  detail,  in  connection 
with  any  mechanical  stoker  now  on  the  market. 

The  idea  of  mechanically  supplying  the  coal  to  the  furnace 
seems  to  have  first  occurred  to  Wm.  Brunton  in  1819.  He 
patented  a  circular  fire  grate,  movable  on  a  vertical  spindle. 

John  Stanley,  in  1822,  patented  means  for  blowing  the  coal 
upon  the  grates  by  means  of  a  fan. 

J.  G.  Bodmer,  in  1834,  patented  the  first  movable  grate. 
The  bars  were  made  to  move  toward  the  rear  of  the  furnace, 
where  they  dropped  singly  upon  rails  and  were  mechanically 
returned  to  the  front. 

John  Juckes,  in  1841,  patented  the  first  " endless  chain"  grate. 

Samuel  Hall,  in  1845,  was  the  first  to  introduce  reciprocating 
inclined  grate  bars  in  connection  with  a  mechanical  stoker. 

T.  and  T.  Vickers,  sometime  in  the  forties,  invented  the 
first  " under-feed"  stoker,  employing  a  ram  to  place  the  fuel  in 
position.  This  machine  was  called  in  ridicule  "a  sausage  stuffer," 
and  the  term  has  clung  to  this  type  of  stoker  ever  since. 

John  Bourne,  about  1857,  was  the  first  to  introduce  the  idea 
of  reducing  the  coal  to  a  fine  powder,  and  blowing  it  in  a  dry 
state  into  the  fire-box,  mixed  with  air,  where  it  was  supposed 
to  burn,  much  after  the  manner  of  gas. 

UNDERFEED   STOKERS 

In  the  under-feed  type  of  stoker,  as  we  have  it  to-day,  the 
fresh  coal  is  forced  by  mechanical  means  from  below,  up  into 
the  bed  of  burning  fuel.  A  steam  ram  is  employed  for  this  pur- 
pose. Air  is  supplied  by  a  fan  and  is  delivered  in  jets  into  the 
green  fuel,  the  theory  being  that  the  volatile  gases  distilled  from 
the  green  coal  by  the  influence  of  the  heat  of  the  burning  fuel 

61 


62  COMBUSTION  AND  SMOKELESS   FURNACES 

above  are  mixed  with  the  oxygen  supplied  by  the  air  jets,  and 
burn  on  their  passage  up  through  the  incandescent  coal.  There 
is  no  doubt  that  such  an  effect  takes  place.  The  coked  fuel 
above  supplies  the  heat,  and  the  air  jets  the  necessary  oxygen. 
Stokers  of  this  type  will  produce  the  best  efficiency  when  they  are 
operated  with  as  little  vacuum  as  possible  in  the  fire-box.  The 
fireman  usually  sets  the  damper  wide  open,  putting  the  full  draft 
of  the  stack  upon  the  furnace.  With  the  chimney  pulling  and 
the  forced  draft  pushing,  the  efficiency  will  be  low.  The  author 
recalls  one  case  where  the  vacuum  in  the  fire-box  was  reduced 
from  55  hundredths  of  an  inch  to  10  hundredths.  This  was  fol- 
lowed by  an  immediate  reduction  in  the  fuel  consumption  of 
more  than  30  per  cent.  It  often  happens  that  seams  and  cracks 
are  formed  in  the  upper  strata  of  fuel,  when  the  green  coal  is 
rammed  into  position  below.  Under  such  circumstances,  the 
volatile  elements  will  escape  and  there  will  be  smoke.  Until  the 
fuel  settles  into  position,  closing  the  cracks,  there  will  be,  of 
necessity,  some  escape  of  free  air  into  the  fire-box.  The  time  and 
extent  of  feeding  fuel  may  be  in  the  control  of  the  boiler  attend- 
ant, or  they  may  be  automatically  regulated  by  the  boiler  pres- 
sure. Clinkers  are  likely  to  form  to  a  considerable  extent,  near 
the  point  of  air  delivery,  and  also  upon  the  dead  plates  which 
are  employed  in  place  of  grates.  Such  clinkers  must  of  necessity 
be  removed  by  hand,  as  in  the  case  of  the  hand-fired  furnace. 
This  constitutes  one  of  the  main  objections  to  the  under-feed 
stoker.  The  under-feed  device  has  both  advantages  and  disad- 
vantages, as  compared  with  other  styles  of  stokers  on  the  market. 


OVERFEED  STOKERS  — THE    "CHAIN    GRATE" 
x 

Among  over-feed  stokers  employing  horizontal  moving  grates, 
the  " endless  chain  grate"  type  seems  to  predominate,  almost 
to  the  point  of  excluding  all  others.  The  coal  is  usually  fed  from 
a  hopper  upon  the  grate,  at  a  point  slightly  forward  of  the  boiler 
front.  An  arch  of  firebrick  or  tile  is  generally  provided  over  the 
forward  end  of  the  grate.  This  arch  becomes  highly  heated, 
and  the  reflected  heat  first  distills  the  volatile  gases  from  the 
fresh  coal,  and  also  assists  in  igniting  the  fuel.  The  fuel  is 


MECHANICAL  STOKERS  63 

carried  slowly  to  the  rear  by  the  moving  grate,  passing  through 
the  various  stages  from  distillation  of  the  volatile  elements  to 
final  combustion  of  the  fixed  carbon.  Advocates  of  this  style 
of  stoker  talk  at  great  length  about  "progressive  combustion," 
a  term  which  does  not  necessarily  carry  any  practical  significance, 
as  all  combustion  is  obviously  "progressive."  It  is  of  great 
importance  to  the  owner  and  operator  of  a  chain  grate  stoker 
that  this  "progressive  combustion"  take  place  in  proper  concord 
with  the  movement  of  the  grate;  otherwise,  one  of  two  extremely 
undesirable  things  will  occur.  The  ash  is  dumped  into  a  pit  at 
the  rear  when  the  chain  grate  makes  its  downward  turn.  It  is 
evident  that  if  combustion  is  not  fully  completed  when  the  dump- 
ing moment  arrives,  unconsumed  fuel  will  be  deposited  along 
with  the  ashes  and  a  direct  loss  will  result.  It  is  also  evident 
that  if  combustion  is  completed  before  the  dumping  moment 
arrives,  the  grate  will  be  bare  in  places  and  cold  air  will  rush  in 
and  affect  efficiency.  To  adjust  the  feed  and  time  the  speed  of 
the  grate  in  such  a  manner  that  combustion  is  fully  completed 
at  the  moment  of  dumping,  and  not  before,  is  a  nice  proposition 
and  requires  a  high  degree  of  vigilance,  experience,  and  expert- 
ness.  It  is  possible,  moreover,  for  the  two  undesirable  results 
mentioned  to  occur  simultaneously.  There  will  be  some  friction 
between  the  fuel  on  the  grate  and  the  side  walls  of  the  furnace. 
This  will  tend  to  retard  somewhat  the  movement  of  the  fuel  that 
is  under  the  influence  of  the  friction.  What  may,  for  want  of  a 
better  term,  be  called  the  "fire  line  "  —  the  line  where  combus- 
tion is  completed  —  will  very  likely  be  irregular,  unconsumed  fuel 
being  dumped  into  the  ash-pit  at  one  or  more  points  and  air 
being  allowed  to  enter  through  bare  spots  at  others.  Boilers 
equipped  with  such  stokers  are  usually  set  detached  or  semi- 
detached, and  a  door  provided  at  the  side  about  midway  of  the 
grate.  This  door  gives  access  for  the  fire  tools  of  the  attendant, 
whose  duty  it  is,  among  other  things,  to  attend  to  the  fire  line, 
keep  the  same  regular  and  at  the  proper  distance  from  the  dump- 
ing point.  The  attendant  must  also  increase  or  diminish,  or 
entirely  stop  the  movement  of  the  grate,  as  occasion  requires, 
in  order  to  keep  the  fire  line  in  the  proper  position.  It  is  neces- 
sary for  the  man  charged  with  these  duties  to  remain  awake. 

Considerable  opportunity  is  always  present  for  the  leakage 
of  air  into  the  fire-chamber.     There  must  be  room  for  "play" 


64  COMBUSTION  AND  SMOKELESS   FURNACES 

between  the  moving  chain  grate  and  the  side  walls  of  the  furnace. 
This  free  space  will  probably  be  covered  with  fuel  throughout  a 
portion  of  its  length,  but  toward  the  rear  of  the  fire-chamber  the 
fuel  will  tend  to  work  away  from  the  side  walls,  leaving  an  open- 
ing that  air  will  be  bound  to  find.  Unless  suitable  provision  is 
made  against  it,  air  will  find  its  way  around  the  rear  of  the  grate 
and  up  into  the  fire-chamber.  Some  air  is  of  course  necessary 
to  the  burning  gases,  and  if  these  leaks  that  we  have  pointed  out 
could  be  properly  proportioned  to  the  demands  of  the  fire-box, 
there  would  be  no  objection  to  them. 

It  is  argued  by  the  manufacturers  of  chain  grate  stokers  that 
the  use  of  their  devices  results  in  a  large  saving  of  labor.  The 
testimony  of  the  boiler  room  will  not  always  bear  out  this  conten- 
tion. It  requires  almost  as  much  muscle  to  get  the  coal  into  the 
hopper  of  the  stoker  as  would  be  required  to  feed  the  ordinary 
hand-fired  furnace.  This  criticism  of  course  does  not  fully  apply 
if  the  coal  is  gravity  carried  to  the  stoker  from  a  point  overhead. 
The  chain  grate  is  somewhat  narrowly  limited  as  to  the  character 
of  the  fuel  that  may  be  successfully  burned.  If  screenings  or  nut 
coal  are  unavailable,  a  coal  crusher  must  be  employed.  There  is 
almost  invariably  and  unavoidably  a  serious  leakage  of  fresh  coal 
through  the  grate,  not  to  mention  a  further  leakage  of  partly 
burned  fuel.  The  green  coal  is  fed  upon  a  bare  grate,  and  some- 
thing of  a  sifting  process  occurs.  The  chain  grate  is  made  up  of 
a  multiplicity  of  small  members,  and  to  avoid  cramping  at  the 
turns  a  freedom  of  movement  between  the  grate  members  is  pro- 
vided for,  which  sometimes  results  in  more  air  space  than  good 
practice  demands.  Such  superfluous  air  space  in  the  grate  does 
not  tend  to  minimize  the  loss  of  coal.  A  deep  pit  is  provided 
beneath  the  grate  and  the  men  in  the  boiler  room  are  well  ac- 
quainted with  it,  if  the  engineer  in  charge  makes  any  pretensions 
as  to  economy.  This  pit  requires  frequent  shoveling  out  and  the 
mixture  of  coal,  cinders,  and  ashes  is  "  burned  over."  Notwith- 
standing any  number  of  "  burnings  over,"  the  final  ash  from  a 
chain  grate  will  usually  contain  some  surprises  in  the  way  of 
combustible. 

INCLINED   GRATE   STOKERS 

This  type  of  stoker  is  furnished  with  an  inclined  grate  surface, 
—  the  inclination  sometimes  extending  from  the  sides  toward 


MECHANICAL  STOKERS  65 

the  center,  and  sometimes  from  the  front  to  the  rear.  The  grate 
members  are  usually  given  a  reciprocal  motion,  which  is  designed 
to  work  the  coal  from  the  hopper  to  the  ash-pit  at  the  bottom, 
as  combustion  proceeds.  Sometimes  this  movement  of  the  coal 
is  faster  than  desirable,  —  {t landslides"  occur,  exposing  the  bare 
grate  and  filling  the  ash-pit  with  unconsumed  fuel.  Sometimes 
the  coal  is  perverse  and  refuses  to  descend,  adhering  to  the  grate 
bars  so  tenaciously  that  the  vigorous  use  of  a  slice  bar  is  required 
to  detach  it.  It  is  claimed  for  this  type  of  stoker  that  more 
grate  surface  can  be  provided  in  proportion  to  the  heating  sur- 
face of  the  boiler  than  with  any  other,  making  an  increase  of 
horse-power  possible,  if  desirable.  All  types  of  stokers  are  more 
or  less  limited  as  to  quality  and  character  of  coal,  the  type  under 
consideration  particularly  so,  as  any  fuel  disposed  to  melt  down, 
or  "slag,"  will  tend  to  adhere  to  the  grates,  while  a  fuel  of  the 
opposite  extreme  will  be  subject  to  "landslide." 

FUEL  SPREADERS 

The  "fuel  spreader"  is  an  uncommon  type  of  stoker,  and  is 
not  entitled  to  very  serious  consideration.  The  coal  is  projected 
upon  the  grates,  sometimes  continuously  and  sometimes  at  in- 
tervals, depending  upon  the  means  employed  and  the  ideas  of 
the  inventor.  A  mechanism  is  sometimes  employed  to  project 
the  coal,  and  other  variations  of  the  idea  make  use  of  a  jet  of 
steam,  drawn  from  the  boiler.  The  "fuel  spreader,"  like  other 
stokers,  has  its  limitations  as  to  character  of  coal  employed. 

PULVERIZED   FUEL   BURNERS 

The  pulverized  fuel  burner  has  so  far  failed  to  score  very 
much  of  a  success.  Coal,  finely  powdered  and  mixed  with  air, 
is  instantaneously  combustible  to  the  point  of  being  explosive. 
If  delivered  to  a  furnace  in  jets,  or  otherwise,  properly  mixed 
with  oxygen,  it  will  burn,  much  after  the  manner  of  a  combustible 
gas.  The  difficulties  in  the  way  of  such  a  device  appear  to  be 
principally  of  a  mechanical  and  practical  nature,  and  the  inventor 
may  yet  be  forthcoming  who  will  solve  them.  The  writer  knows 
of  nothing  of  the  kind  at  present,  sufficiently  well  demonstrated 
along  practical  lines,  to  warrant  serious  consideration  by  the 
coal  consumer. 

AUTHOR'S  NOTE:  Since  this  book  was  published  in  1906  the 
4 'fuel  spreader"  has  been  developed  into  a  practical  device. 


66  COMBUSTION    AND   SMOKELESS    FURNACES 

AS  TO  STOKERS  IN  GENERAL 

The  mechanical  stoker  unquestionably  has  its  field,  and  has 
no  doubt  entered  the  engineering  world  to  stay.  The  best  of 
such  devices  is,  however,  far  from  the  pinnacle  of  perfection,  and 
the  purchaser  will  do  well  to  investigate  the  field  carefully  before 
buying.  The  initial  cost  is  necessarily  heavy,  and  the  cost  of 
maintenance  is  an  item  to  be  gravely  considered.  If  mechanical 
means  are  provided  to  get  the  fuel  into  the  hopper  of  the  stoker, 
a  considerable  saving  of  labor  will  result.  If  the  shovel  is  relied 
upon,  the  small  saving  of  labor  effected  will  be  fully  offset  by  the 
increased  care  necessitated  in  order  to  insure  anything  like  fair 
results.  The  limitations  as  to  quality  of  coal  are  factors  to  be 
taken  into  account.  Most  stokers  are  designed  to  burn  " slack" 
or  "  screenings,"  and  while  these  grades  of  coal  are  usually  ob- 
tainable, when  desired,  it  is  not  to  be  assumed  that  they  invariably 
will  be.  As  a  matter  of  insurance  against  shut-downs  for  want 
of  suitable  fuel,  the  plant  employing  mechanical  stokers  should 
be  equipped  with  a  coal  crusher. 


CHAPTER  VII 

HAND-FIRED    FURNACES  —  MECHANICAL    DRAFT 

MECHANICAL  draft  has,  under  many  circumstances,  much  to 
recommend  it.  Under  certain  circumstances  it  is  almost  a  neces- 
sity, —  as  for  instance  when  anthracite  coal,  particularly  dust, 
is  burned  for  power  purposes,  or  when  great  increase  of  horse- 
power is  necessary,  irrespective  of  efficiency.  Mechanical  draft, 
when  applied  to  a  boiler  furnace,  may  be  either  " forced"  or 
''induced,"  i.e.,  air  may  be  forced  by  fan  or  otherwise  under  the 
grates,  the  ash-pit  doors  being  sealed;  or  the  contents  of  the 
breeching  may  be  exhausted  and  draft  "induced,"  the  atmos- 
pheric pressure  supplying  the  increased  draft  in  its  effort  to  fill 
the  vacuum.  The  increased  oxygen  supplied  by  either  means 
greatly  hastens  the  consumption  of  coal  and  increases  the  avail- 
able horse-power  of  the  boiler,  though  not  necessarily  in  pro- 
portion to  the  increased  coal  consumption.  It  is,  of  course, 
fully  as  necessary  to  supply  air  to  the  gases  in  the  fire-box  when 
mechanical  draft  is  employed,  as  in  the  case  of  natural  draft. 
If  such  air  is  not  supplied,  combustion  may  be  just  as  incomplete 
as  under  any  other  circumstances.  Where  mechanical  draft, 
especially  forced  draft,  is  employed,  a  surplus  of  air  may  be  ex- 
pected to  find  its  way  through  the  fuel  on  the  grates,  and  this 
surplus  is  often  sufficient  to  supply  the  needs  of  combustion. 
If  efficiency  is  had  in  mind,  the  difficulty  at  once  arises  of  keeping 
such  air  supply  down  to  the  needs  of  the  fire-box.  If  the  de- 
mands are  exceeded,  waste  of  heat  units  is  bound  to  result.  The 
ideal  system  of  mechanical  draft  will  deliver  a  portion  of  the  air 
supply  above  the  fire,  and  this  portion  will  be  under  automatic 
control  to  meet  the  general  conditions  in  the  fire-box,  set  out  by 
the  diagram,  Fig.  2.  Where  such  arrangement  is  in  effect,  suffi- 
cient fuel  should  be  carried  upon  the  grates  to  insure  the 
absence  of  air  holes.  Some  power  is  of  course  necessary  to  accom- 
plish mechanical  draft,  but  this  outlay  of  energy  may  be  more 

67 


68  COMBUSTION  AND  SMOKELESS   FURNACES 

than  offset  by  employing  the  waste  heat  of  the  escaping  gases 
for  some  practical  purpose.  Temperature  in  the  chimney  is 
necessary  where  natural  draft  is  relied  upon,  as  the  temperature 
is  the  cause  of  the  draft,  but  in  the  case  of  mechanical  draft, 
such  temperature,  while  it  may  be  of  assistance,  is  not  necessary. 
Advocates  of  mechanical  draft  lay  great  stress  upon  the  claimed 
saving  in  installation,  as  against  a  natural  draft  plant.  This 
saving  is  effected  by  the  smaller  chimney  required.  Mechanical 
draft  can  get  along  without  any  chimney  at  all,  if  necessary, 
while  with  natural  draft  the  chimney  is  one  of  the  principal 
items  of  cost.  It  should  be  remembered  that  a  chimney,  if 
properly  built,  will  last  indefinitely,  and  is  not  subject  to  depre- 
ciation, while  the  same  cannot  be  said  of  the  machinery  incident 
to  any  system  of  mechanical  draft.  The  chimney,  if  carried 
high  enough  and  properly  proportioned,  will  produce  any  amount 
of  draft  desired.  Public  health  demands  a  high  chimney,  as  it 
is  advisable  to  discharge  the  gases  resulting  from  combustion, 
as  high  up  into  the  air  as  possible.  The  smoke  from  a  tug-boat 
or  locomotive  does  more  damage  to  health  and  property  than 
that  discharged  from  a  factory  chimney,  and  municipal  regula- 
tions should,  among  other  things,  insist  upon  high  stacks.  With 
the  small  steam  plant,  there  is  no  doubt  that  cost  of  installation, 
adequate  chimney  included,  is  in  favor  of  natural  draft.  There 
is  room  for  so  much  argument  pro  and  con  of  mechanical  draft, 
so  many  factors  entering  into  the  situation,  that  the  owner  of 
the  power  plant  will  do  well  to  give  the  subject  most  careful 
consideration  before  abandoning  natural  draft. 

Jets  of  steam  are  sometimes  employed  for  the  purpose  of 
assisting  draft.  The  cost  of  installation  in  such  case  is  very 
light  and  constitutes  the  only  argument  in  its  favor.  The  steam 
required  to  operate  such  a  device  to  any  degree  of  efficiency  as  a 
draft  accelerator  represents  an  expenditure  for  fuel  far  in  excess 
of  the  interest  charge  on  the  cost  of  equipping  the  plant  with  a 
fan-blower  system. 

All  those  devices  which  return  the  escaping  smoke  to  the 
fire-box  or  ash-pit,  for  the  purpose  of  consuming  it,  must  be 
considered  under  the  head  of  mechanical  draft.  It  is  difficult 
to  imagine  a  sane  argument  in  support  of  the  use  of  such  a  device, 
smoke  consumption  being  in  mind,  when  the  market  affords 
others  capable  of  consuming  the  smoke  and  gases  before  they 


HAND-FIRED  FURNACES  69 

leave  the  combustion  chamber.  If  it  can  be  shown  that  the  re- 
turn to  the  fire-box  of  a  portion  of  the  gases  carried  by  the 
breeching  tends  to  lower  the  temperature  of  the  gases  in  the 
chimney  without  affecting  the  rate  at  which  coal  may  be  burned 
upon  the  grate,  and  if  the  amount  of  saving  represented  by  such 
lowering  of  stack  temperature  exceeds  all  the  costs  that  may 
be  legitimately  charged  against  the  operation  of  such  a  device, 
then  there  are  good  arguments  in  its  favor.  The  author  recently 
inspected  a  device  of  the  kind  under  consideration.  The  en- 
gineer of  the  plant  presented  very  satisfactory  evidence  that  he 
was  saving  fuel  as  well  as  reducing  smoke.  The  saving  was 
partly  attributable  to  the  burning  of  the  combustible  gases 
returned  but  mainly  attributable  to  the  use  of  the  heated  oxy- 
gen returned  with  the  gases.  A  considerable  surplus  of  air 
was  being  passed  through  the  furnace.  This  meant  considerable 
highly  heated  oxygen  in  the  flue  gases,  which  on  being  returned 
to  the  furnace  reduced  the  requirement  for  fresh  air,  thereby 
reducing  the  excess  air.  Efficiency  was  increased  as  the  air 
excess  was  reduced  and  the  heat  units  returned  with  the  flue 
gases  were  just  that  much  gain.  There  are  certain  types  of 
boilers,  to  which  such  an  arrangement  might  be  well  adapted, — 
an  internally  fired  boiler  of  the  marine  type  for  instance,  which, 
owing  to  its  construction,  prohibits  the  use  of  any  arch  or  other 
accessory  to  the  furnace  proper,  to  aid  in  combustion.  It  has 
been  proposed  by  several  inventors  to  absorb  the  heat  of  the 
escaping  gases  by  a  system  of  air  pipes  within  or  a  box  arrange- 
ment about  the  breeching, — the  air  heated  in  this  manner  being 
supplied  to  the  furnace  by  a  blower.  Such  plan  has,  in  fact, 
been  employed  with  gratifying  results.  A  French  inventor 
carried  it  to  the  extreme  by  taking  his  air  supply  from  near  the 
top  of  the  stack  and  conducting  it  through  a  sheet  metal  flue  down 
the  chimney  and  through  the  breeching  to  the  boiler  furnace.  It 
is  quite  needless  to  say  that  the  Frenchman's  plan  proved  im- 
practical. 

NATURAL  DRAFT 

Most  " smokeless  furnaces"  are  to  be  found  in  the  field  of 
hand-fired  boilers  employing  natural  draft.  This  is  necessarily  the 


70  COMBUSTION  AND  SMOKELESS   FURNACES 

case,  as  such  boilers  largely  predominate  and  always  will  be  in  the 
majority.  The  salesman  for  the  mechanical  stoker  and  mechanical 
draft  appliance  finds  his  most  fruitful  field  among  large  power 
plants  making  new  installations.  These  plants  are  vastly  in  the  mi- 
nority, and  greater  popular  interest  attaches,  accordingly,  to  the 
field  we  are  about  to  consider,  which  interest  provides  excuse  for 
the  more  extended  notice  of  the  devices  peculiar  to  this  field. 

"STEAM  JETS" 

It  is  impossible  for  the  author  to  give  honest  expression  to 
any  views  favorable  to  the  use  of  the  "steam  jet."  Such  a 
statement,  at  the  outset,  necessitates  a  close  examination  of 
these  devices. 

"Steam  jets,"  by  a  wide  margin,  constitute  a  majority  of  the 
devices  to  regulate  smoke  and  improve  combustion,  upon  which 
the  United  States  Patent  Office  has  issued  Letters  Patent,  since 
the  smoke  problem  began  to  claim  the  attention  of  the  inventor. 
Scarcely  a  week  passes  that  does  not  see  an  increase  in  the  brood. 
It  is  hard  to  find  a  boiler  in  Chicago,  in  service  for  any  length  of 
time,  that  has  not  had  experience  with  one  or  more  of  these  make- 
shift appliances.  It  is  hard  to  find  language  sufficiently  acrid 
to  do  justice  to  the  "steam  jet,"  for  its  use  constitutes  a  crime 
against  good  engineering.  Something  may  be  said  in  favor  of 
almost  every  other  class  of  smoke-consuming  appliance,  but  the 
writer  is  unable  to  discover  a  single  redeeming  feature  in  the 
whole  horizon  of  "steam  jets."  If  such  redeeming  feature  exists, 
it  lies  in  the  low  initial  cost  of  such  an  appliance.  No  doubt 
this  item  of  low  cost  has  had  much  to  do  with  the  wide-spread 
use  of  this  type  of  "smoke  consumer."  It  must  be  admitted 
that  the  use  of  a  "  steam  jet,"  if  properly  applied  and  operated,  will 
tend  to  satisfy  the  smoke  inspector;  its  effects  upon  combustion, 
however,  as  a  flue  gas  analysis  will  show,  are  counterfeit  and 
consist  more  in  appearances  than  actuality.  The  cost  of  sup- 
plying the  steam  to  operate  such  a  make-believe  appliance  is  so 
great  that  the  man  who  pays  the  coal  bill  could  not  afford  its 
use,  if  paid  handsomely  to  permit  the  equipment  of  his  boilers. 
It  is  obligatory  upon  the  writer  to  furnish  very  valid  reasons  for 
the  employment  of  such  sweeping  criticisms. 

Objections  to  the  use  of  a  "steam  jet"  may  be  catalogued 
as  follows: 


HAND-FIRED   FURNACES  71 

1st.  The  cost  of  supplying  steam  to  operate  such  a  device 
is  prohibitive. 

2d.  The  steam  introduced  absorbs  heat,  and  lowers,  to  the 
extent  of  such  absorption,  the  efficiency  of  the  boiler. 

3d.  If  directed  against  the  fuel  bed,  escaping  carbonic  acid 
gas  is  reactively  converted  to  carbon  monoxide,  and  heat  is 
absorbed  in  the  operation.  Carbon  monoxide  is  also  directly 
formed  by  contact  between  steam  and  incandescent  coke,  and 
unless  free  oxygen  is  admitted  to  the  fire-box,  this  gas  escapes, 
entailing  a  further  loss.  The  conversion  of  carbon  monoxide 
in  this  manner  entails  a  loss  of  heat,  and  the  water  vapor  resulting 
from  the  reunion  of  the  released  hydrogen  of  the  steam  with 
oxygen  absorbs  still  more  heat.  The  released  hydrogen  also 
combines  with  carbon  to  form  marsh  gas,  and  such  combination 
absorbs  heat. 

4th.  The  floating  soot  in  the  smoke  is  precipitated  and  de- 
posited upon  the  shell  and  tubes  of  the  boiler  in  the  form  of  scale. 
Such  scale  is  impregnated  with  sulphur,  and  " pitting"  of  boiler 
shell  and  tubes  is  likely  to  occur. 

5th.  Escaping  oxides  of  sulphur  are  converted  to  vapors 
of  sulphurous  and  sulphuric  acid. 

6th.  The  grates  are  robbed  of  draft,  clinkers,  and  burned  out 
grate  bars  result. 

7th.  The  noise  attendant  upon  the  use  of  a  " steam  jet"  is 
almost  insufferable. 

8th.  The  use  of  " steam  jets"  may  impair  efficiency  to  such 
an  extent  that  additional  boiler  capacity,  boiler  room,  and  labor 
will  have  to  be  provided. 

Let  us  see  how  far  this  catalogue  of  objections  can  be  sub- 
stantiated: 

If  the  engineer  who  is  employing  a  " steam  jet"  believes  he  is 
using  a  negligible  amount  of  steam  for  the  purpose,  let  him  con- 
dense the  steam  from  the  jets  for  a  day  and  weigh  the  resulting 
water.  Then  let  him  divide  the  quantity  of  water  taken  by  his 
boiler  during  the  day  into  the  result,  and  treat  himself  to  a  sur- 
prise. It  is  only  by  such  tests  as  these  that  we  can  arrive  at  the 
extent  of  losses  and  savings  in  an  intelligible  manner.  An  off- 
hand estimate  is  never  reliable. 

In  1890,  tests  were  made  at  the  United  States  Navy  Yard, 
Brooklyn,  New  York,  to  determine  the  efficiency  of  various 
patented  steam  jet  devices  offered  the  government.  The  tests 
were  conducted  by  the  chief  of  the  Bureau  of  Engineering  of  the 
United  States  Navy.  The  steam  to  operate  the  jets  was  drawn 
from  a  separate  boiler,  used  for  the  time  being  for  no  other  pur- 


72  COMBUSTION  AND  SMOKELESS   FURNACES 

pose.  It  was  found  that  the  jets  consumed  steam  amounting 
from  8.2  per  cent,  to  21.2  per  cent,  of  that  generated  by  the  boiler 
to  which  they  were  applied.  The  steam  from  one  of  the  jets, 
having  a  nozzle  one  sixteenth  of  an  inch  in  diameter,  was  con- 
densed and  a  pound  of  water  resulted  in  two  minutes.  This  is 
almost  equivalent  to  one  horse-power.  Steam  is  usually  con- 
ducted from  the  boiler  to  the  jets  through  a  pipe  not  less  than 
one-half  inch  in  diameter.  If  enough  jets  are  employed  to  equal 
the  capacity  of  the  pipe,  as  is  often  the  case,  the  loss  entailed  is 
quite  a  formidable  matter. 

The  writer  knows  of  many  cases  where  tests  have  been  made 
to  determine  the  amount  of  steam  consumed  by  jet  devices,  and 
in  no  instance  has  such  consumption  been  less  than  10  per  cent, 
of  the  generated  horse-power  of  the  boiler.  The  figures  average 
nearer  15  per  cent,  if  the  jets  are  operated  to  the  extent  of 
having  any  appreciable  effect  upon  the  appearance  of  the  smoke. 

The  Chicago  Tribune,  in  reporting  an  address  delivered  by 
Chief  Smoke  Inspector  Schubert  of  the  Chicago  Boiler  Inspection 
Department,  at  a  banquet  of  the  Commercial  Club,  says: 

"He  criticised  'steam  jets'  as  makeshifts,  and  advised  against 
their  installation,  as  they  consume  from  10  to  15  per  cent,  of  the 
steam  generated,  for  their  operation." 

That  the  use  of  a  " steam  jet"  entails  a  serious  loss  of  power, 
is  a  fact  so  easily  ascertainable  by  any  one  interested,  that  further 
discussion  would  be  superfluous. 

The  second  criticism  offered  above  should  require  no  argu- 
ment for  its  substantiation.  Steam  is  not  combustible,  neither 
does  it  in  any  way  aid  in  combustion,  when  supplied  in  this  man- 
ner. It  must  be  heated  to  the  temperature  of  the  escaping  gases 
and  such  an  operation  results  in  the  absorption  of  heat  units 
and  a  corresponding  lowering  of  the  efficiency  of  the  boiler.  It 
is  undeniable  that  steam  is  composed  of  hydrogen  and  oxygen, 
that  hydrogen  in  its  free  state  is  a  highly  combustible  gas,  con- 
taining approximately  62,000  British  thermal  units  per  pound; 
that  oxygen  is  the  supporter  of  combustion  and  the  fire  will 
flourish  when  oxygen  is  present;  and  that  water  or  steam  may 
be  decomposed  into  its  elements  in  the  fire-box.  It  does  not 
follow,  however,  as  many  advocates  of  "steam  jets"  fondly  be- 
lieve, that  any  gain  of  heat  units  can  result  from  the  burning  of 


HAND-FIRED   FURNACES  73 

the  hydrogen,  decomposed  in  the  fire-box  from  its  union  with 
oxygen.  Berthollet's  Second  Law  applies,  as  we  have  already 
pointed  out.  As  much  heat  is  absorbed  in  the  decomposition 
of  the  steam  as  is  generated  by  burning  the  hydrogen  after  de- 
composition occurs.  The  product  of  the  combusion  of  hydrogen 
is  water.  If  hydrogen  could  be  injected  into  the  fire-box  in  its 
free  state  and  without  drawing  upon  the  heat  of  the  furnace  for  its 
isolation,  the  proposition  would  be  an  entirely  different  one.  All 
" water  gas"  arguments  advanced  in  favor  of  " steam  jets"  may 
accordingly  be  dismissed  as  entirely  unworthy  of  consideration. 

In  connection  with  the  third  criticism  upon  "  steam  jets," 
we  would  revert  to  the  report  of  Eckley  B.  Coxe,  published  in 
the  transactions  of  the  New  England  Cotton  Manufacturers 
Association,  previously  noticed.  The  result  of  Coxe's  tests  upon 
the  " steam  jet"  bears  out  the  contentions  of  the  author  in  his 
third  criticism,  and  also  stands  in  proof  of  what  has  been  said 
concerning  the  relative  efficiencies  of  the  fan  and  steam  blower 
system  of  mechanical  draft.  Now  let  us  see  how  the  chemical 
reactions  claimed  under  the  third  head  occur,  when  jets  of  steam 
are  directed  into  the  fire-box.  More  or  less  carbonic  acid  gas 
will  be  escaping  from  the  incandescent  fuel.  If  the  jets  are 
directed  against  the  fuel,  this  gas,  (C02),  will  be  forced  back  into 
the  carbon,  where  it  will  pick  up  another  atom  of  that  element, 
and  (C2O2),  or  (CO),  carbon  monoxide,  will  result.  This  reactive 
formation  absorbs  heat  as  the  tendency  is  away  from  instead 
of  toward  combustion  or  oxidization.  If  a  jet  of  steam  is  directed 
against  coke  at  a  low  red  heat,  practically  pure  hydrogen  and 
carbonic  acid  gas  will  result,  —  the  reaction  being  as  follows: 

2  (H20)  +  C  =  2  (H2)  +  (C02) 

If,  however,  the  coke  is  incandescent  the  reaction  is  somewhat 
different  and  is  as  follows: 

(H.O)  +  C  =  (By  +  (CO) 

The  following  reaction  may  also  result  from  the  union  of  the 
released  hydrogen  with  carbon: 

2  (H2)  +  C  =  (CHJ 

The  formula,  (CH4),  stands  for  marsh  gas,  or  light  car- 
buretted  hydrogen.  All  the  above  formations  represent  ab- 

AUTHOR'S  NOTE:  The  reaction  of  incandescent  carbon  upon  C02  is  usu- 
ally expressed  by  the  following  equation: 

C02  +  C  =  2  (CO). 

It  is  not  positively  known  how  the  steps  in  this  reaction  proceed.  It 
has  been  held  by  some  chemists  that  an  unstable  molecule  (C202)  is  formed, 
which  is  at  once  broken  down  into  two  molecules  of  CO. 


74  COMBUSTION  AND  SMOKELESS   FURNACES 

sorption  of  heat,  and  the  efficiency  of  the  boiler  is  lowered  by  the 
extent  of  such  absorption.  If  these  gases  are  burned  by  the 
admission  of  free  oxygen,  the  absorbed  heat  is  of  course  restored, 
but  no  net  gain  to  the  boiler  can  be  argued  from  the  combustion 
of  any  gases  so  formed.  All  of  the  above  contentions  will  be 
substantiated  by  any  standard  authority  on  chemistry. 

As  to  the  fourth  criticism,  the  following  is  offered:  It  often 
happens  when  coal,  particularly  dry  "  slack,"  is  shoveled  into  the 
bin,  that  the  dust  is  almost  unbearable.  The  engineer  or  fireman 
turns  a  jet  of  steam  into  the  bin,  and  the  loose  dust  or  carbon 
floating  in  the  air  is  moistened  by  the  steam  vapor  and  is  settled 
or  precipitated  to  the  floor.  The  effect  of  a  "  steam  jet "  upon  the 
loose  soot  or  particles  of  carbon  floating  in  the  furnace  gases  is 
the  same.  It  is  precipitated  upon  the  shell  and  tubes  of  the  boiler 
in  the  form  of  "scale."  The  writer  has  seen  scale  a  quarter  of 
an  inch  thick  in  the  fire-tubes  of  a  tubular  boiler,  due  to  the  use 
of  a  "  steam  jet."  The  scale  was  so  hard  and  tenacious  that  nothing 
short  of  "reaming"  sufficed  to  remove  it.  It  was  found  upon 
examination  that  the  tubes  were  corroded  to  the  danger  point 
by  the  action  of  the  sulphur  compounds  contained  in  the  scale, 
and  every  tube  in  the  boiler  was  condemned  and  removed.  There 
had  been  large  diminution  in  the  draft  of  the  boiler  in  question, 
and  this  diminution  was  correctly  charged  to  the  reduced  area 
of  the  tubes,  due  to  the  scale.  Some  inventors  of  "steam  jet" 
appliances  are  honest  enough  to  call  their  devices  "smoke  bleach- 
ers" or  "washers,"  and  such  appellations  are  well  chosen.  Ob- 
serve the  effect  when  the  wind  is  in  the  right  direction  to  blow 
the  steam  from  the  exhaust  funnel  at  the  top  of  the  building 
into  the  smoke  issuing  from  the  stack.  The  black  carbon  will 
to  a  greater  or  less  extent  be  "  washed  out "  of  the  smoke.  Every 
one  has  noticed  that  there  is  less  color  in  the  smoke  when  a  loco- 
motive is  running  under  steam  than  when  the  steam  is  shut  off 
and  the  engine  is  slowing  down.  This  is  due  to  the  fact  that  the 
steam  exhaust  discharges  into  the  smoke-stack. 

As  to  the  fifth  criticism,  little  need  be  said  in  support  of  it. 
All  bituminous  coal  contains  more  or  less  sulphur.  When  this 
element  is  oxidized,  the  product  is  sulphur  dioxide,  (SO2).  This 
is  a  gas,  but  it  is  soluble  in  water,  and  when  it  encounters  steam 
or  water  vapor  under  the  boiler  or  in  the  chimney  gases,  the 
following  reaction,  resulting  in  sulphurous  acid,  occurs: 


HAND-FIRED   FURNACES  75 

(H20)  +  (S02)  =  (H2S03) 

If  another  atom  of  oxygen  is  added,  the  result  is  (H2S04),  or 
sulphuric  acid.  Everybody  knows  what  sulphurous  or  sulphuric 
acid  will  do  to  iron  or  steel.  There  is  more  or  less  moisture  in 
all  grades  of  soft  coal,  and  more  or  less  water  vapor  entrained  in 
the  atmosphere.  Some  sulphurous  or  sulphuric  acid  is,  accord- 
ingly, unavoidably  formed.  It  is  bad  practice  to  multiply  the 
evil  by  blowing  unnecessary  moisture,  in  the  form  of  steam,  into 
the  furnace  gases. 

With  reference  to  the  sixth  criticism,  it  need  only  be  said  that 
the  boiler  flues,  breeching,  and  stack  are  forced  to  accommodate 
the  steam  delivered  to  the  furnace  by  the  jet,  and  to  the  extent 
of  the  volume  of  such  steam  the  draft  of  air  through  the  grates 
is  diminished.  If  sufficient  steam  is  introduced  to  have  an  ap- 
preciable effect  upon  the  color  of  the  smoke,  the  impairment  of 
draft  will  be  such  as  to  work  damage  to  the  grates.  If  the  steam 
is  not  turned  off,  either  by  hand  or  otherwise,  between  firings, 
the  damage  resulting  to  grates  will  be  still  more  aggravated.  It 
is  often  urged,  and  with  some  reason,  that  the  use  of  a  "  steam 
jet  "  tends  to  a  softening  of  the  clinkers.  Substantially  the  same 
softening  results  will  be  attained  if  the  ash  pit  is  kept  supplied 
with  a  quantity  of  water.  Draft  impairment  means  clinkers,  and 
anything  beyond  a  moderate  use  of  the  "  steam  jet,"  means  draft 
impairment.  The  "  steam  jet "  will  do  well  if  it  succeeds  in 
softening  the  clinkers  for  which  it  is  itself  responsible. 

Every  one  who  has  seen  a  "steam  jet"  in  operation  will  agree 
that  the  seventh  criticism  is  well  taken. 

Acceptance  of  the  eighth  objection  follows  upon  admission 
of  the  correctness  of  the  preceding  criticisms.  If,  for  instance, 
the  plant  is  equipped  with  ten  boilers,  all  supplied  with  "steam 
jets,"  and  the  consumption  of  steam  to  operate  the  jets  is  10 
per  cent.,  then  the  plant  has  the  effective  horse-power  of  nine 
boilers,  and  if  this  is  not  sufficient,  additional  boilers  will  have 
to  be  provided.  "But,"  the  advocate  of  the  "steam  jet"  may 
argue,  "we  have  increased  the  horse-power  of  the  boiler  since 
equipping  it  with  the  'steam  jet'  device."  If  the  steam  should 
be  delivered  exclusively  above  the  grates,  such  statement  could 
have  no  foundation  in  fact.  If  the  delivery  should  be  below  the 
grates,  forced  draft  would  result  to  some  extent  and  increased 


76  COMBUSTION  AND  SMOKELESS   FURNACES 

horse-power  might  occur.  Any  such  increase  of  horse-power 
would  necessarily  be  attended  by  a  decrease  in  efficiency  to  the 
extent  of  making  the  increased  power  a  very  expensive  matter. 

All  of  the  authorities  are  in  agreement  with  respect  to  the 
undesirability  of  the  "  steam  jet.7'  One  or  two  will  be  quoted. 
Walter  B.  Snow,  in  his  " Steam  Boiler  Practice/'  says: 

"The  case  of  the  'steam  jet'  may  be  briefly  summarized 
thus:  It  has  the  advantage  of  costing  very  little  to  put  in  and 
keep  in  repair.  Its  disadvantages  are,  first,  it  requires  a  very 
large  amount  of  steam  to  run  it;  second,  it  introduces  a  large 
amount  of  water  or  steam,  all  of  which  has  to  be  heated  and 
carried  up  the  chimney;  third,  unless  very  carefully  managed 
there  is  a  large  development  of  carbonic  oxide  (CO),  hydrogen, 
and  marsh  gas,  due  to  the  dissociation  of  the  water,  which  has  a 
tendency  to  carry  off  a  great  deal  of  heat  in  the  stack;  fourth,  the 
intensity  of  draft  produced  by  this  means  is  distinctly  limited; 
and  fifth,  the  noise  incident  to  its  use  is  at  times  excessive." 

D.  K.  Clark,  a  well-known  British  engineering  author,  who 
was  himself  the  inventor  of  a  " steam  jet"  apparatus,  is  forced  to 
conclusions  unfavorable  to  the  use  of  such  a  device.  With 
respect  to  a  test  made  upon  his  own  contrivance,  he  tells  us  that 
the  evaporation  was  7.35  Ib.  of  water  with  the  jet  in  operation, 
and  7.10  with  the  jet  off.  He  does  not  tell  us  what  amount  of 
steam  the  jet  consumed  in  its  operation.  It  certainly  must  have 
been  far  in  excess  of  the  slight  gain  in  evaporation,  which  could 
be  accounted  for,  perhaps,  by  atmospheric  conditions  or  other 
agencies  having  no  connection  with  the  device. 

The  same  author  tells  us  of  a  " steam  jet"  device  patented  by 
M.  W.  Ivison  in  1838,  which  was  discredited  after  careful  tests, 
as  wasting  fuel,  although  it  was  conceded  smoke  was  "  stopped." 
He  tells  us  also  of  tests  made  upon  a  device  patented  in  1858  by 
M.  Emil  Burnat,  a  French  inventor.  In  this  case,  "  smoke  pre- 
vention" was  complete,  but  the  efficiency  was  lowered  8  per 
cent. 

An  examination  of  the  United  States  Patent  records  develops 
the  fact  that  over  75  per  cent,  of  the  patents  issued  in  the  last 
seventeen  years  on  " smoke-consuming"  appliances  have  been 
granted  on  modifications  of  the  "steam  jet."  The  inventor  has 
blown  steam  into  every  conceivable  part  of  the  furnace,  com- 
bustion chamber,  smoke-box,  breeching,  and  chimney.  The  most 


HAND-FIRED   FURNACES 


77 


common  form  of  the  " steam  jet"  is  illustrated  in  Fig.  5.  Other 
points  of  steam  admission,  preferred  by  various  inventors,  are 
indicated  by  the  letters  "a,"  "b,"  "c,"  etc.  Less  objection,  of 
course,  attaches  to  the  introduction  of  steam  into  the  breeching, 
or  chimney,  as  compared  with  points  preceding  the  escape  of  the 
gases  from  the  boiler.  Soot,  and  scale  deposits,  will  do  less 
damage  to  the  breeching  and  stack  than  to  the  shell  and  tubes 
of  the  boiler. 

Air  is  often  blown  or  "  siphoned,"  as  the  inventor  usually 
expresses  it,  into  the  fire-box  by  a  "  steam  jet,"  and  the  air  in  such 
case  naturally  assists  in  combustion.  The  nearer  such  combina- 
tion device  comes  to  relying  upon  the  agency  of  air,  and  the 
further  it  gets  away  from  the  use  of  a  jet,  the  less  objections 


I 


FIG.  5 


there  are  to  it.  The  objections  become  still  fewer  in  number 
when  the  use  of  the  jet  is  discarded  altogether.  Many  "steam 
jets"  employ  an  automatic  mechanism  to  turn  on  the  steam 
when  the  furnace  is  stoked  and  turn  it  off  again  after  a  certain 
period  elapses.  Such  an  arrangement  of  course  tends  to  make 
a  bad  matter  a  little  less  obnoxious.  If  the  jet  is  not  constantly 
in  use,  the  tip  is  liable  to  be  fused  over  and  the  engineer  has  an 
unnecessary  annoyance  added  to  his  list  of  troubles,  most  of 
which  are  unavoidable. 

The  writer  dismisses  the  "steam  jet"  with  the  feeling  that  a 
disagreeable  duty  has  been  honestly  performed  in  the  interests 
of  good  engineering. 


78  COMBUSTION  AND  SMOKELESS   FURNACES 

AIR  FURNACES 

The  term  "air  furnaces,"  which  is  of  the  author's  own  coinage, 
is  meant  to  include  all  those  devices,  applicable  to  hand-fired 
boilers  employing  natural  draft,  which  introduce  air  into  the 
fire-box  or  elsewhere  beyond  the  grates,  for  the  purpose  of  pro- 
moting the  combustion  of  the  gases  originating  from  the  fuel. 
What  has  been  said  concerning  the  necessity  of  "air  regulation  " 
applies  impartially  to  all  the  various  types  of  devices  that  remain 
to  be  considered.  No  device  should  be  considered  by  the  coal 
consumer  unless  it  is  equipped  with  means  to  accomplish  such 
air  regulation.  No  air  regulating  mechanism  can  be  considered 
as  meeting  the  conditions,  moreover,  unless  it  is  "adjustable" 
by  experiment  to  meet  any  combination  of  conditions  that  may 
result  in  a  change  of  demand  as  to  air,  either  in  quantity  or  in 
manner  of  admission.  The  broad  statement  may  be  safely  made 
that  improved  combustion,  coupled  with  proper  air  regulation, 
means  an  increase  in  efficiency,  —  the  extent  of  such  increase 
being  determined  by  the  extent  of  the  improvement  in  combus- 
tion; while  improved  combustion,  even  to  the  extent  of  burning 
the  last  atom  of  the  combustible,  may,  and  probably  would  be, 
attended  by  a  loss  of  efficiency  in  the  absence  of  proper  regula- 
tion of  the  air  admitted. 

GRATE  ADMISSION 

The  difficulty  of  introducing  the  proper  amount  of  free  oxygen 
to  the  fire-box  through  the  grates  has  already  been  pointed  out. 
Some  air  furnaces  employ  what  is  known  as  the  "alternate" 
system  of  firing.  One  side  of  the  furnace  is  fired  with  fresh  fuel, 
and  the  heat  of  the  incandescent  fuel  on  the  other  side  is  relied 
upon  for  "temperature,"  it  being  expected  that  sufficient  free 
air  will  find  its  way  through  the  partly  burned  out  bed  of  coke, 
to  supply  the  necessary  oxygen  to  the  combustible  gases  released 
from  the  fresh  fuel.  It  is  manifest  that  if  air  is  to  be  supplied 
in  this  manner,  a  degree  of  care  and  expertness  must  be  employed 
in  stoking,  not  usually  encountered  in  the  fire-room.  It  is  also 
evident  that  more  air  will  be  admitted  as  the  fresh  fuel  approaches 
the  coking  point  where  the  demand  for  oxygen  is  small,  than 
immediately  after  firing  when  the  demand  is  at  the  maximum. 
The  longer  the  coked  fuel  remains  without  the  addition  of  fresh 


HAND-FIRED   FURNACES 


79 


coal,  the  more  opportunities  the  air  will  find  to  work  its  way 
through  it.  There  are  many  practical  reasons  why  such  an  ar- 
rangement for  air  admission  is  not  the  ideal  one,  although  it  has, 
in  connection  with  the  method  of  firing  necessarily  employed, 
much  in  its  favor.  It  is  impossible,  however,  to  approach  any- 
thing like  correct  air  regulation,  with  a  furnace  of  this  character. 
The  scale  of  air  admission  will  be  the  reverse  of  the  correct  one 
as  indicated  by  Fig.  2,  and  the  fireman  would  be  indeed  fortunate 
if  able  to  so  regulate  the  fuel  bed  that  the  same  quantity  of  air 
would  be  admitted  at  each  firing. 

Hollow  grate  bars  were  early  employed  for  air  admission, 


FIG.  6 

the  air  being  sometimes  delivered  from  the  front  end  of  the  grates 
near  the  dead-plate,  and  sometimes  from  the  rear,  through  the 
bridge  wall.  The  idea  of  the  inventors  of  such  grates  seems  to 
have  been  that  the  air  would  be  to  some  extent  superheated  in 
passing  through  the  hot  grate  bars. 

FIRE-DOOR  ADMISSION 

J.  J.  Roberton,  of  Glasgow,  seems  to  have  been  the  first  to 
supply  air  to  the  fire-box  by  way  of  the  fire-doors.  He  patented 
a  special  door  for  that  purpose  in  1800.  He  supplied  the  coal 
to  the  furnace  by  means  of  a  hopper.  It  was  allowed  to  coke 
in  the  front  of  the  fire-box  and  was  then  pushed  back  to  the  rear. 

Fig.  6,  showing  a  horizontal  cross-section  of  a  furnace  and 


80  COMBUSTION  AND  SMOKELESS   FURNACES 

boiler  setting,  will  serve  to  illustrate  the  objections  that  may  be 
advanced  against  this  manner  of  air  admission.  The  oppor- 
tunities for  thorough  admixture  of  the  air  with  the  gases  are  not 
what  they  might  be,  if  admission  is  after  this  manner.  The  air 
enters  in  substantially  an  undivided  stream,  which  bores  its  way 
through  the  gases  of  the  fire-box.  If  the  door  should  be  provided 
with  a  "grid,"  the  air  would  be  diffused  to  some  extent  and  the 
objection  would  not  be  as  sweeping  as  otherwise.  There  is  always 
"dead  water"  behind  the  center  pier  and  abutments  of  a  swing 
bridge,  and  there  will  be  "dead"  space  between  the  fire-doors 
and  also  at  the  sides.  It  is  not  maintained  that  intermixture  of 
air  with  all  the  gases  of  the  fire-box  cannot  be  effected  in  this 
manner,  in  time  to  accomplish  their  combustion,  but  it  is  a  fact 
that  cannot  be  disputed  that  such  intermixture  necessitates  a 
larger  surplus  of  air  than  will  be  required  when  admission  is 
accomplished  in  some  other  manner,  making  possible  a  greater 
diffusion  of  the  air.  Air  entering  through  the  fire-doors  comes 
from  one  of  the  lowest  strata  in  the  boiler  room,  and  is  therefore 
the  coldest  air  obtainable.  All  other  things  being  equal,  prefer- 
ence should  be  given  to  the  device  that  takes  its  air  at  the  highest 
initial  temperature.  The  use  of  the  fire-door  for  air  admission 
makes  hand  manipulation  necessary  to  regulate  the  supply,  and 
such  manner  of  regulation  is  not  to  be  considered  when  auto- 
matic means  can  be  supplied.  The  movable  nature  of  the  fire- 
door  precludes  the  practical  attachment  of  any  automatic  mech- 
anism. The  low  cost,  and  ease  of  providing  air  through  the 
fire-doors,  are  the  greatest  arguments  in  favor  of  the  plan. 

SIDE-WALL  ADMISSION 

Figs.  7,  8,  and  9  are  referred  to  in  connection  with  what  will 
be  said  concerning  devices  admitting  air  into  the  fire-box  through 
the  side  walls  of  the  furnace.  Such  furnaces  are  open  to  two 
objections;  First,  they  fail  as  smoke  consumers,  owing  to  the 
impossibility  of  mixing  the  air  so  introduced  with  the  gases; 
second,  the  walls  of  the  furnace  and  boiler  setting  are  seriously 
weakened  and  damaged  by  the  building  of  air  ducts  therein, 
the  installation  of  hollow  tile,  or  other  factors  necessary  to  the 
device. 

Consideration  of  Fig.  7  will  make  plain  the  reasons  for  the 
first  objection.  The  air  entering  the  fire-box  is  caught  at  once 

AUTHOR'S  NOTE:  Automatic  door  closing  mechanisms  have  been  used 
with  some  success, — the  apparatus  being  arranged  to  close  the  furnace  door 
in  a  predetermined  interval  of  time.  While  such  an  arrangement  tends 
to  introduce  the  air  in  a  diminishing  volume  as  suggested  by  the  diagram, 
Fig.  2,  the  distribution  of  the  air  so  introduced  is  not  satisfactory. 


HAND-FIRED    FURNACES 


81 


by  the  draft  and  carried  back  along  the  side  walls  of  the  boiler 
and  no  opportunity  is  given  for  intermixture  with  the  gases. 
The  air  jets  from  the  side  walls  enter  the  fire-box  at  right  angles 
to  the  draft  of  the  furnace.  No  other  result  than  that  indicated 
by  the  arrows  in  the  drawing  referred  to  can  be  expected.  The 
gases  in  the  center  of  the  fire-box  receive  no  oxygen,  and  without 
that  element  they  cannot  be  consumed. 

The  havoc  worked  to  the  boiler  walls  by  these  side-wall  de- 
vices will  be  better  understood  when  the  common  method  of 
setting  a  boiler  is  explained.  The  " setting"  of  an  ordinary 
multitubular  boiler  usually  consists  of  two  walls,  an  exterior 
and  interior.  Each  wall  is  about  nine  inches  thick,  and  the  side 
of  the  interior  wall  exposed  to  the  fire  is  lined  with  fire-brick. 
An  air  space,  "C,"  separates  the  walls  and  serves  the  purpose 


y///7///////7//^ 

?//////r//?/^^^ 


///////////////^^^ 


FIG.  7 

of  insulating  the  boiler  against  the  escape  of  heat.  The  interior 
walls  support  the  entire  weight  of  the  boiler.  Now,  in  order  to 
install  tile  air  ducts,  or  build  air  passages  in  the  side  walls  of  the 
furnace,  it  is  necessary  to  tear  away  the  brickwork  of  the  wall 
"B,"  see  Figs.  7  and  9,  supporting  the  forward  lugs  of  the  boiler. 
It  is  an  impossibility  to  replace  these  walls  in  as  good  condition 
as  they  were  originally,  after  such  undermining  operations  have 
taken  place.  An  examination  of  the  side  walls  of  a  boiler  em- 
ploying such  a  device  will  in  nine  cases  out  of  ten  develop  a 
crack,  running  up  and  to  the  rear  at  about  the  forward  face  of 
the  bridge  wall,  as  illustrated  in  Fig.  8.  It  will  be  a  piece  of  good 
luck  if  the  front  end  of  the  boiler  has  not  settled  to  the  extent  of 
requiring  re-setting.  Every  engineer  understands  the  dangers 
arising  from  scale,  etc.,  when  a  boiler  settles  by  the  forward  end. 


82 


COMBUSTION  AND  SMOKELESS   FURNACES 


Even  if  it  were  possible  to  properly  rebuild  the  walls  after  the 
installation  of  such  air  chambers,  the  existence  of  these  hollow 
ducts  or  passages  in  what  is  intended  to  be  a  solid  wall  of  masonry, 
capable  of  sustaining  great  weight,  would  materially  weaken  it. 
If  the  boiler  setting  is  old,  or  improperly  constructed  in  the  first 
place,  the  building  of  such  a  device  practically  amounts  to  the 
wrecking  of  the  walls.  The  portion  of  the  walls  undermined  and 
weakened  must  sustain  a  weight,  when  the  boiler  is  in  operation 
and  full  of  water  to  the  working  line,  of  from  eight  to  twelve  tons. 
No  engineer,  alive  to  the  welfare  of  the  plant  entrusted  to  his 
care,  will  permit  the  building  of  any  such  device  in  connection 
with  his  boilers.  Such  contrivances  have  nothing  whatever  in 


FIG.  9 

their  favor.  If  the  boiler  is  suspended  independently  of  the  set- 
ting, as  it  should  be,  but  too  infrequently  is,  the  walls  of  the  set- 
ting may,  of  course,  be  attacked  with  less  danger  to  the  boiler. 

BRIDGE  WALL  ADMISSION 

The  bridge  wall  has  been  employed  for  air  admission  since 
time  immemorial  in  the  history  of  smokeless  furnaces.  There 
are  many  things  to  recommend  the  use  of  the  bridge  for 'this 
purpose.  There  are  also  valid  arguments  against  it.  No  damage 
can  be  worked  to  the  boiler  or  setting  by  any  amount  of  recon- 
struction of  the  bridge.  The  air  is  heated  to  some  extent  upon 
its  passage  up  through  the  bridge,  and  it  may  be  delivered  across 
the  entire  width  of  the  fire-box.  The  bridge  is  also  located  at 
the  point  where  the  highest  temperature  exists,  and  this  is  in  its 
favor.  Let  us  now  look  at  the  objections  to  the  use  of  the  bridge 


HAND-FIRED    FURNACES 


83 


wall  and  the  things  to  be  guarded  against  if  it  is  employed  for 
air  admission. 

Unless  "extraordinary  means  are  employed  to  heat  the  air 
prior  to  admission,  it  will  enter  the  fire-box  at  a  temperature 
below  that  of  the  furnace.  If  colder  than  the  gases,  the  air  will 
tend  to  seek  the  lower  strata  while  the  gases  will  find  the  upper 
ones.  It  accordingly  follows  as  a  conclusion,  that  the  air  should 
be  introduced  above  the  fire,  for  in  such  case  the  tendencies  of 
the  air  and  gases  to  find  their  respective  levels  will  lead  to  an 
intermixture.  Now,  if  air  is  delivered  through  the  bridge  wall, 
it  will  enter  below  rather  than  above  the  gases,  and  admixture 
will  take  place  only  to  the  extent  that  the  air  and  gas  currents 


FIG.  10 

come  into  contact  with  each  other.  There  will  be  a  current  of 
unoxidized  gas,  passing  over  the  bridge,  next  to  the  boiler,  and 
a  sheet  of  air,  cooler  than  the  gases,  passing  over  the  bridge,  below 
the  gas  currents. 

Fig.  10  illustrates  some  of  the  points  employed  for  delivering 
air  from  the  bridge.  There  are  obstacles  in  the  way  of  using  any 
one  of  the  points,  "A,"  "B,"  or  "C,"  or  for  that  matter  any 
other  point  upon  the  surface  of  the  bridge,  for  air  delivery.  If, 
for  instance,  air  should  be  delivered  from  the  face  of  the  bridge 
wall,  as  at  "A,"  the  discharge  openings  would  soon  become 
fouled  with  slag,  or  clinkers,  and  the  device  incapacitated  for 
further  service.  When  the  bridge  wall  is  low,  as  is  often  the 
case,  the  fuel  will  at  times  accumulate  to  a  height  covering  the 
air  openings,  and  slag  will  attach.  If  the  openings  should  be  at 


84  COMBUSTION  AND  SMOKELESS   FURNACES 

a  sufficient  height  above  the  grates  to  preclude  contact  with  the 
fuel,  more  or  less  slag  would  still  attach,  as  the  flames  are  laden 
with  non-combustible  matter,  ash,  etc.,  which  would  adhere 
upon  contact  with  the  brickwork  of  the  bridge.  The  entire 
front  face  of  the  bridge  wall  is  subject  to  slag  and  clinkers,  and 
there  is  no  way  to  avoid  them.  If  the  air  openings  should  be 
at  the  top  of  the  bridge,  as  at  "B,"  there  would  be  a  deposit  of 
ashes  in  addition  to  the  slag,  and  the  openings  would  not  remain 
very  long  in  commission.  When  the  openings  are  upon  the  rear 
of  the  bridge,  as  at  "C,"  delivery  of  air  is  too  late  to  meet  the 
requirements  of  combustion.  There  will  of  course  be  no  diffi- 
culty at  this  point  from  slag,  and  if  the  openings  are  near  the  top 
of  the  bridge,  little  liability  to  stoppage  from  ashes. 

In  gase  of  air  delivery  from  either  side  walls  or  bridge  wall, 
the  logical  place  from  which  to  take  the  air  supply  will  be  the 
ash-pit.  Air  taken  from  this  source  means  robbery  of  the  grates, 
and  this  should  not  be  allowed,  if  avoidable.  There  will  be  great 
difficulty  in  applying  any  automatic  air-regulating  mechanism 
to  air  ducts  in  either  side  walls  or  bridge  wall. 

As  between  the  three  methods  of  air  delivery  noticed,  the 
advantages  lie  with  the  fire-doors. 

ARCH   ADMISSION 

Many  devices  employ  an  arch,  or  arches,  for  the  purpose  of 
air  admission.  Such  arches,  if  properly  placed  and  constructed, 
are  superior  to  any  of  the  means  already  noticed,  —  the  air  in 
such  cases  being  delivered  above  the  fire  and  the  air  openings 
being  so  located  that  there  is  very  little  if  any  danger  of  ob- 
structions by  accumulation  of  slag,  or  otherwise.  There  are, 
however,  special  objections  which  apply  to  the  use  of  arches  in 
certain  positions,  and  these  will  be  considered  at  the  proper 
time.  Air  is  sometimes  delivered  to  the  fire-box  from  a  chamber, 
built  into  the  brickwork  above  the  fire-doors,  and  sometimes  an 
air  chamber  is  formed  between  this  brickwork  and  an  arch  dis- 
posed in  front  of  it,  the  air  being  delivered  from  the  chamber  into 
the  fire-box  in  a  sheet  or  in  a  number  of  jets.  Such  constructions 
have  very  distinct  advantages,  but  these  advantages  in  them- 
selves are  not  sufficient  to  justify  claims  of  superiority,  if  other 
necessary  factors  are  absent,  while  being  present  in  the  competing 
device  of  another  form  of  construction. 


HAND-FIRED    FURNACES  85 

MISCELLANEOUS 

Under  the  head  of  "Miscellaneous  "  may  be  included  all 
those  nondescript  devices  that  introduce  air  at  various  points 
in  the  combustion  chamber.  Air  introduction,  posterior  to  the 
bridge  wall,  is  too  late  to  be  of  much  assistance  in  combustion. 
The  gases  chill  to  some  extent,  in  passing  from  the  fire-box  to 
the  combustion  chamber,  and  it  is  better  practice  to  ignite  them 
before  they  enter  the  combustion  chamber.  It  is  obvious  that 
an  intermixture  of  air  must  precede  ignition.  While  it  is  possible 
to  provide  such  an  arrangement  of  arches  and  " retorts"  in  the 
combustion  chamber,  as  to  make  combustion  of  the  gases  possible 
after  passing  the  bridge,  all  such  structures  are  undesirable. 
There  should  be  no  impediments  at  the  rear  of  the  bridge  to  the 
easy  and  frequent  removal  of  ash  accumulations.  The  nearer 
combustion  takes  place  to  the  forward  end  of  the  boiler,  the 
better,  as  the  hot  gases  have  that  much  more  distance  to  travel 
in  contact  with  the  heating  surfaces  of  the  boiler,  and  heat  ab- 
sorption will  be  correspondingly  greater. 

FIRE  ARCH   FURNACES 

There  are  so  many  modifications  of  fire  arch  furnaces  that 
it  is  difficult  to  make  a  differentiating  classification.  They  may 
be  classified  broadly  as,  first,  furnaces  with  arches  above  the 
grates;  second,  arches  above  the  bridge  wall;  third,  arches  in 
the  combustion  chamber. 

Furnaces  with  arches  above  the  grates  may  be  subdivided 
into  those  with  arches  covering  the  entire  grate  surface,  and 
those  with  narrow  arches  disposed  above  the  grates,  usually  at 
a  short  distance  from  the  bridge  wall. 

The  purposes  of  these  arches,  which  are  variously  known 
as  "fire,"  "retort,"  "igniting,"  or  "baffle"  arches,  are  to 
reflect  the  heat  of  the  fire  upon  the  gases  and  thus  produce  a 
high  temperature;  to  prevent  chilling  contact  of  the  gases  with 
the  boiler  shell,  and  to  bring  the  gases  into  contact  with  the 
incandescent  fuel.  Some  styles  of  arches  also  serve  the  purpose 
of  improving  the  mixture  of  the  air  with  the  gases.  We  will 
first  notice  the  furnace  with  the  arch,  covering  substantially 
the  entire  grate. 

In  the  case  of  this  class  of  arch,  one  of  the  objects  aimed  at 


86 


COMBUSTION   AND  SMOKELESS   FURNACES 


—  the  production  of  a  high  temperature  —  is  certainly  attained. 
All  furnace  arches  are  necessarily  constructed  of  refractory 
material,  usually  of  firebrick  or  fire  clay  tile,  which  has  a  large 
capacity  for  absorbing  and  storing  heat.  This  heat  is  returned 
upon  the  fuel  bed,  and  the  temperature  resulting  is  excessive, 
usually  far  more  than  is  demanded  for  the  combustion  of  the 
gases.  If  air  is  admitted  in  sufficient  amount,  and  mixed  with 
the  gases,  combustion  follows  as  a  matter  of  fact,  provided  suffi- 
cient room  exists  for  the  expansion  of  the  gases  while  in  the  act 
of  combustion,  and  provided  agencies  are  not  present  to  check 
combustion  when  the  burning  gases  leave  the  influence  of  the 
arch.  An  arch  of  the  kind  under  consideration  is  illustrated  in 
Fig.  11.  Unless  means  are  provided  to  prevent  it,  the  gases  will 


m 


FIG.  11 

strike  the  boiler  shell  immediately  upon  leaving  the  arch  and 
experience  sufficient  chill  to  cause  the  precipitation  of  unoxidized 
carbon.  When  fresh  coal  is  thrown  upon  the  rear  of  the  grate, 
the  gases  arising  will  not  receive  much  benefit  from  the  arch  and 
will  likely  escape  unconsumed.  Arches  at  the  rear  of  the  bridge 
wall  are  often  employed  in  connection  with  this  kind  of  device, 
and  do  much  to  counteract  the  tendencies  mentioned.  Some 
inventors  have  gone  so  far  with  this  type  of  construction  as  to 
extend  the  arch  the  entire  length  of  the  boiler;  some  even  invert 
the  arch  and  bolt,  or  otherwise  secure  it,  to  the  boiler  shell. 

The  objections  to  this  style  of  arch  are  numerous  and  serious. 
One  of  the  evils  to  which  it  is  subject  comes  from  the  oversurplus 
of  heat.  The  fireman  who  can  work  in  front  of  a  furnace  so 


HAND-FIRED    FURNACES  87 

equipped  is  a  sort  of  a  modern  Shadrach.  Coal  contains  more 
or  less  foreign  and  non-combustible  matter.  If  the  heat  of  the 
fire-box  is  too  high,  this  foreign  matter  fuses  into  a  clinker  before 
the  fixed  carbon  or  coke  part  of  the  fuel,  which  burns  slowly,  is 
consumed.  A  portion  of  the  unconsumed  carbon  fuses  in  with 
the  clinker,  and  is  so  much  fuel  lost.  The  fireman  will  require 
no  argument  as  to  the  undesirability  of  clinkers,  and  he  has  little 
use  for  a  device  that  tends  to  manufacture  them.  They  mean 
lost  fuel,  lost  efficiency,  and  extra  labor.  The  non-combustible 
foreign  matter  should  be  left  as  ash,  instead  of  clinkers,  and  is 
left  principally  in  that  form  when  combustion  of  the  fixed  carbon 
is  complete.  There  can  be  no  argument  as  to  economy  in  favor 
of  burning  the  gases,  if  waste  of  the  fixed  element  of  the  fuel  is 
to  result.  Clinkers,  moreover,  do  not  tend  to  improve  grate 
bars,  and  are  in  every  particular  an  undesirable  quantity.  The 
clinker  evil,  with  a  furnace  of  this  kind,  is  not  so  marked  where 
a  high-grade  fuel  is  burned,  but  it  will  exist  to  some  extent  if 
excessive  heat  is  present,  no  matter  what  the  fuel.  If  the  use 
of  such  an  arch  is  attended  by  an  excess  of  air  supply  above  the 
fire,  the  evils  as  to  grates  and  clinkers  are  emphasized,  as  every 
cubic  foot  of  excess  air  tends  to  suppress  the  movement  of  a  like 
amount  through  the  grates.  If  excess  heat  occurs  in  the  fire-box, 
considerable  energy  will  be  lost  by  radiation  through  the  boiler 
front,  and  the  fire-door  " liners"  and  all  metal  work  about  the 
boiler  front  are  liable  to  suffer,  either  by  fusing  or  warping,  from 
the  excess  of  heat.  The  writer  has  even  seen  fire-doors  warped 
so  badly,  where  such  an  arch  was  employed,  that  they  had  to 
be  discarded. 

Examination  of  Fig.  11  will  convince  the  reader  that  one 
effect  of  an  arch  covering  the  fire-box  is  to  insulate  the  heating 
plates  at  the  forward  end  of  the  boiler  from  the  heat  of  the  fire- 
box. Some  heat  will,  of  course,  be  communicated  to  the  boiler 
shell  through  the  arch,  but  the  amount  will  be  inconsiderable 
as  compared  with  what  the  plates  would  receive  in  the  absence 
of  such  an  arch. 

Builders  of  such  furnaces  will  of  course  claim  that  there  is 
nothing  in  this  contention,  but  it  may  be  easily  proved  by  noting 
the  time  necessary  to  raise  steam  from  a  cold  boiler  with  such 
device,  and  comparing  with  the  time  required  to  get  up  steam 
with  the  ordinary  furnace. 


88  COMBUSTION  AND  SMOKELESS   FURNACES 

The  heat  stored  in  such  an  arch  will  be  sufficient  to  keep  the 
boiler  under  steam  for  an  indefinite  period  after  the  fire  is  banked 
or  drawn,  making  a  watch  upon  the  boiler  necessary  until  the 
arch  has  cooled.  The  writer  knows  of  an  instance  where  a  boiler 
equipped  with  such  device  showed  a  gage  pressure  of  80  Ib. 
on  Monday  morning,  after  having  been  shut  down  on  the  Friday 
evening  previous.  The  safety  valve  had  been  popping  at  inter- 
vals in  the  meantime,  and  the  water,  which  had  been  left  at  a 
high  level,  was  down  at  the  danger  line. 

Such  an  arch  of  course  tends  to  keep  the  cold  air,  rushing  in 
at  the  fire-doors  at  the  time  of  stoking  or  cleaning  fires,  from 
contact  with  the  boiler  shell  until  heated  to  a  considerable  ex- 
tent, and  this,  with  many  engineers,  will  constitute  quite  an  argu- 
ment in  its  favor.  The  slow  rate  at  which  the  boiler  may  be 
heated  up  or  cooled  off  also  has  some  advantages,  the  welfare 
of  the  boiler  being  in  mind. 

The  fireman  will  usually  object  to  any  arch  construction  over 
the  fire-box,  for  the  reason,  among  others,  that  it  offers  some 
obstructions  to  the  use  of  his  fire  tools.  If  the  boiler  is  set  low, 
as  many  boilers  are,  such  an  arch  will  tend  to  materially  restrict 
the  area  of  the  fire-chamber.  With  the  most  careful  handling 
of  the  fire  tools,  it  will  be  abraded  more  or  less,  and  cannot  be 
expected  to  be  a  very  long-lived  structure,  particularly  if  built 
of  brick,  and  the  low  point  presented  by  the  downward  curve 
of  the  boiler  precludes  the  use  of  thick  arch  blocks.  If  brick- 
work is  to  be  interposed  between  the  grates  and  boiler,  the  ad- 
vantage accordingly,  with  respect  to  room,  appears  to  lie  with 
the  inverted  arch,  bolted  or  otherwise  attached  to,  or  supported 
by,  the  boiler  shell.  Such  construction,  however,  has  its  own 
peculiar  disadvantages,  which  will  suggest  themselves  to  any 
engineer. 

Fig.  12  illustrates  a  very  effective  form  of  arch  if  smoke  con- 
sumption is  the  main  object  in  mind.  This  construction  is  often 
referred  to  as  the  "McGinnis  arch,"  taking  its  name  from  the 
inventor  who  first  employed  it.  As  the  patents  have  expired, 
it  may  be  built  without  fear  of  infringement,  if  desired,  and  with 
careful  stoking  may  be  made  to  answer  the  demands  of  the  smoke 
inspector.  The  arch  shown  in  Fig.  13  may  be  employed  to  some 
good  purpose  in  connection  with  this  form  of  construction,  but 
very  distinct  disadvantages  are  suffered  by  its  use. 


HAND-FIRED    FURNACES 


89 


The  method  of  firing  employed  in  conjunction  with  the 
"McGinnis  arch"  is  as  follows:  The  fresh  coal  is  fired  near  the 
dead  plate,  and  after  coking  is  pushed  back  against  the  bridge 
wall  and  beneath  the  arch,  and  another  supply  of  green  fuel 
placed  in  position  for  coking.  The  volatile  gases  are  drawn  away 
from  contact  with  the  boiler  shell  by  the  draft,  passing  down  and 
under  the  arch.  These  gases  are  subjected  to  high  temperature, 
on  passage  between  the  hot  arch  and  the  incandescent  fuel 
beneath,  and  if  the  correct  distances  between  arch,  fuel  bed,  and 
bridge  wall  have  been  observed  and  the  proper  amount  of  air 
admitted  and  mixed  with  the  gases  before  they  arrive  at  the  arch, 
combustion  will  be  complete,  or  relatively  so. 


FIG.  12 

The  objections  to  the  " McGinnis"  type  of  arch  are  not  so 
numerous  as  those  cited  against  the  construction  last  discussed. 
Such  objections  as  do  exist,  however,  are  quite  marked.  There 
will  be  little  heat  thrown  out  in  the  face  of  the  fireman  and  sub- 
stantially no  insulation  of  the  forward  part  of  the  boiler  shell. 
There  is  a  distinct  limitation  as  to  the  methods  of  firing  that  may 
be  employed,  and  it  cannot  be  denied  that  the  " coking"  system 
necessitated  imposes  some  extra  labor  upon  the  fireman.  The 
arch  is  very  much  in  the  way  of  cleaning  operations,  and  con- 
siderable clinkering  will  occur  upon  the  grate,  between  the  line 
of  the  forward  face  of  the  arch  and  the  bridge  wall.  The  arch 
will  prove  a  very  short-lived  structure  and  require  frequent  re- 
building, as  repairs,  owing  to  the  nature  of  the  case  are  out  of 
the  question.  Air  supply  is  usually  admitted  by  way  of  the  fire- 


90 


COMBUSTION  AND  SMOKELESS   FURNACES 


doors.     Objections  to  this  form -of  admission  have  already  been 
pointed  out. 

The  most  common  among  the  arches  employed  in  the  com- 
bustion chamber  is  illustrated  in  Fig.  13.  This  arch  is  usually 
employed  as  accessory  to  some  other  form  of  construction,  and 
is  here  discussed,  for  the  reason  that  it  was  a  constituent  part  of 
the  original  "McGinnis  furnace."  The  office  of  the  arch  is  to 
divert  the  gases  from  the  cold  shell  of  the  boiler.  The  deflection 
of  the  gas  currents  also  serves  to  complete  the  mixture  of  the 
air  with  the  gases,  if  such  admixture  has  not  fully  taken  place 
before  the  arch  is  reached.  Any  arrangement  that  will  secure 
complete  mixture  before  the  bridge  wall  is  passed  is  of  course 


FIG.  13 

preferable.  Ignition  should  occur  at  or  near  the  bridge,  as  the 
gases  then  have  the  use  of  the  entire  combustion  chamber  in 
which  to  expand  and  give  up  their  heat  to  the  boiler. 

An  extremely  bad  effect  of  the  " baffle"  arch  is  illustrated 
in  Fig.  13.  The  course  of  the  gases  after  contact  with  the  arch 
is  about  as  shown  in  the  illustration,  and  a  marked  loss  of  effi- 
ciency is  the  result.  It  is  desired  to  apply  the  heat  of  the  gases 
to  the  plates  of  the  boiler  and  not  to  the  floor  of  the  combustion 
chamber.  It  has  been  estimated  by  careful  engineers  that  such 
an  arch  will  impair  efficiency  to  the  extent  of  at  least  10  per  cent. 
An  observing  experience  with  it  will  lead  any  one  to  about  this 
conclusion.  That  the  course  of  the  gas  currents  is  substantially 
as  shown  in  Fig.  13  may  be  settled  by  a  look  into  the  combustion 
chamber  when  the  furnace  is  in  operation.  A  sight  hole  for  this 


HAND-FIRED    FURNACES  91 

purpose  may  be  drilled  in  the  door  to  the  combustion  chamber, 
at  the  rear  of  the  boiler.  To  avoid  the  diversion  of  the  gases 
from  the  heating  plates  of  the  boiler,  the  arch  is  sometimes 
provided  with  apertures  or  "  checker-board  work,"  through 
which  the  gases  stream  along  lines  parallel  to  the  boiler.  Such 
arrangement  tends  to  neutralize  the  work  of  the  arch,  as  com- 
bustion, it  has  been  demonstrated,  is  promoted  by  concentration 
of  the  gas  currents,  and  any  tendency  to  break  up  these  cur- 
rents leads  to  the  opposite  effect.  Such  apertures  are  disposed 
to  become  clogged  with  ashes  in  a  short  time,  when  the  gas  cur- 
rents will  to  a  great  extent  take  the  direction  shown  in  the  illus- 
tration. 

It  can  be  readily  understood  that  the  heat  immediately  in 
front  of  such  an  arch  is  far  greater  than  at  the  rear.  The  arch, 
as  it  is  usually  placed,  is  about  flush  on  its  forward  face  with 
the  boiler  seam,  "a,"  Fig.  13.  The  arrangement  of  the  heating 
plates  of  the  boiler  may  be  such  that  no  seam  occurs  in  this  neigh- 
borhood, but  such  seam  will  usually  be  found  in  about  the  locality 
indicated.  When  the  boiler  plate,  "b,"  is  subjected  to  a  high 
degree  of  heat  and  a  relative  expansion,  and  the  plate,  "c,"  to 
lower  heat  and  less  expansion,  but  one  thing  can  happen  to  the 
seam  and  rivets  at  "a."  They  will  be  subjected  to  terrific  strain, 
and  if  leaks  are  not  started  in  a  short  time  it  will  not  be  the  fault 
of  the  arch.  If  found  necessary  to  use  the  arch  illustrated  in 
Fig.  13,  it  would  be  well  to  construct  a  secondary  bridge  wall 
at  the  rear  of  the  arch  to  redivert  the  gas  currents  and  bring 
them  into  contact  again  with  the  boiler  plates. 

The  purposes  performed  by  the  arches  illustrated  in  Figs. 
11  and  12  are  accomplished  by  those  devices  which  employ  an 
arch  over  the  bridge  wall,  and  an  arch  in  this  position  is  not 
subject  to  the  objections  cited  against  the  other  constructions. 
The  heat  reflected  and  radiated  from  such  arch  will  be  directed 
against  the  bridge  wall  where  no  harm  can  result.  The  grates 
will  not  suffer  and  there  will  be  no  tendency  to  clinkers.  If  the 
arch  and  bridge  are  properly  constructed  with  reference  to  each 
other  and  to  the  draft,  and  air  is  supplied  in  the  proper  manner, 
there  will  be  no  question  as  to  the  combustion  of  the  gases,  as 
ample  temperature  will  exist  in  the  passage  between  the  arch 
and  bridge. 

The  following  difficulties  arise  in  connection  with  all  arches, 


92  COMBUSTION  AND  SMOKELESS   FURNACES 

no  matter  where  located  under  the  boiler,  although  these  diffi- 
culties are  more  pronounced  with  arches  located  over  the  fire- 
box, as  they  are  subjected  to  a  higher  degree  of  heat. 

When  the  arch  becomes  heated,  it  necessarily  expands  and 
exerts  a  tremendous  pressure  upon  the  side  walls  of  the  boiler 
setting,  at  and  above  the  points  where  the  "skewbacks"  of  the 
arch  are  located.  This  pressure  may  be  sufficient  to  displace  the 
walls  from  contact  with  the  boiler.  The  writer  has  seen  such 
results  due  to  an  arch. 

Nearly  all  forms  of  furnace  arches  are  short-lived.  This  is 
largely  due  to  the  contraction  and  expansion  to  which  the  arches 
are  subject,  in  connection  with  the  displacement  of  the  walls 
against  which  the  "skewbacks"  are  placed.  A  very  slight  move- 
ment upon  the  part  of  the  walls  supporting  the  arch  will  be 
sufficient  to  bring  the  arch  down,  when  cooling  and  contraction 
occurs,  as  the  walls  will  not  spring  back  into  position  to  take  up 
the  contraction  of  the  arch.  It  is  advisable  to  employ  some  form 
of  reinforcement  against  the  lateral  thrust  of  the  arch. 

From  the  foregoing,  it  will  appear  that  the  subject  of  furnace 
arches  is  one  that  involves  many  considerations,  and  that  the 
arches  in  most  common  use  are  open  to  many  and  often  vital 
objections.  The  igniting  or  deflecting  arch,  above  or  forward 
of  the  bridge,  may  be  regarded  as  a  necessity,  however,  where 
the  best  results  as  to  smokelessness  are  desired.  The  purchaser 
must  exercise  his  judgment  in  the  selection  of  a  device,  and 
choose  that  one  which  is  best  adapted  to  his  boiler  and  presents 
the  least  number  of  objectionable  features.  As  a  general  proposi- 
tion, that  arch  which  presents  the  least  surface  above  the  grates 
and  which  is  least  in  the  way  of  the  operations  of  the  fireman, 
is  the  one  to  select. 

A  modification  of  the  arch  above  the  bridge  wall  is  some- 
times found  in  a  "  checker-board "  construction,  extending  in 
some  instances  from  the  grates  to  the  boiler.  There  is  nothing 
to  recommend  such  an  arrangement.  The  same  argument  ap- 
plies that  has  been  advanced  against  the  perforated  baffle  arch. 
There  is  tendency,  also,  to  bottle  up  too  much  heat  in  the  fire-box. 

DUTCH   OVEN  FURNACES 

The  " Dutch  oven"  furnace  is  illustrated  in  Fig.  14.  This 
device,  which  is  in  more  or  less  common  use,  consists  of  a  furnace 


HAND-FIRED    FURNACES 


93 


located  outside  and  usually  in  front  of  the  boiler  setting.  It  is 
of  course  necessary  to  provide  the  furnace  with  a  roof  of  refrac- 
tory material.  Firebrick  arch  blocks  are  usually  employed. 
The  objections  that  have  been  pointed  out  against  the  use  of  an 
arch  over  the  fire-box  apply  with  equal  weight  to  the  "  Dutch 
oven."  It  is  always  a  clinker  maker  and  gives  the  fireman  a 
foretaste  of  the  inferno.  It  requires  extra  room,  and  its  con- 
struction involves  considerable  expense.  There  is  also  liability 
of  considerable  loss  from  the  radiation  of  heat.  This  may  be 
reduced  to  the  minimum  by  proper  construction  and  installation. 
A  " Dutch  oven"  should  not  be  employed  if  any  other  device 
will  answer  the  purpose.  There  are  cases,  however,  where  it  is 
the  only  expedient,  and  one  that  it  will  be  advisable  to  employ, 


FIG.  14 

notwithstanding  the  objections  that  go  with  it.  In  the  case,  for 
instance,  of  such  a  boiler  as  is  illustrated  in  Fig.  3,  a  furnace  of 
this  type  is  about  the  only  effective  resource  available,  if  hand 
firing  is  to  be  employed.  The  same  is  to  a  great  extent  true  of 
the  internally  fired  boiler,  —  notably  the  marine  boiler.  Coking 
chambers  are  sometimes  employed  in  conjunction  with  a  "Dutch 
oven"  furnace.  These  will  be  treated  under  the  head  of  "Down- 
Draft  Furnaces." 

DOWN-DRAFT  FURNACES 

The  "down-draft"  furnace  is  by  no  means  a  modern  engi- 
neering invention.  Both  Watt  and  Franklin  designed  forms  of 
furnaces  employing  the  "down-draft"  principle,  and  their  ideas 


94 


COMBUSTION  AND  SMOKELESS   FURNACES 


have  not  been  greatly  improved  upon,  except  in  details  of  con- 
struction. Fig.  15  illustrates  in  a  general  way  the  most  common 
type  of  this  style  of  device  now  on  the  market. 

Two  grates  are  usually  employed  in  the  " down-draft"  fur- 
nace, as  shown  in  the  illustration.  Coal  is  fired  upon  the  upper 
grate,  which  is  composed  of  widely  separated  bars  or  water  tubes. 
The  draft  enters  through  the  open  fire-door  and  passes  down 
through,  first,  the  green,  freshly  fired  coal,  and  then  the  ignited 
portion.  The  theory  is  that  the  gases  distilled  from  the  green 
coal  are  mixed  with  air,  and  ignited  and  burned  while  being 
passed  through  the  underlying  incandescent  fuel.  After  the 
coal  is  coked,  it  is  expected  to  drop  through  the  grates  upon  the 
second  grate,  which  may  be  composed  of  ordinary  straight  bars 


EGF 


FIG.  15 

and  set  up  in  the  usual  manner.  The  combustion  of  the  coke 
or  fixed  carbon  is  completed  upon  this  second  grate.  It  can  be 
seen  that  such  a  furnace  has  somewhat  narrow  limitations  with 
respect  to  coal.  If,  for  instance,  the  coal  is  too  fine,  it  will  fall 
through  upon  the  second  grate  before  coking  is  completed,  and 
there  will  be  smoke.  If  the  coal  is  too  coarse,  it  will  not  pass 
through  the  upper  grate  after  coking  is  completed,  and  the  fire- 
man will  be  compelled  to  rub  it  through  with  a  fire  tool.  If  this 
is  done  at  a  time  when  uncoked  coal  is  upon  the  upper  grate, 
some  of  it  will  probably  accompany  the  coke  to  the  lower  grate, 
and  there  will  be  smoke.  If  it  is  desired  at  any  time  to  force  the 
furnace  to  meet  an  extra  demand  for  steam,  coal  must  either  be 
thrown  direct  upon  the  lower  grate,  or  the  uncoked  fuel  upon 


HAND-FIRED    FURNACES  95 

the  " coking  grate"  must  be  forced  through  upon  the  lower  grate 
in  order  to  make  room  for  a  fresh  supply  of  green  coal.  In  either 
case  there  will  be  smoke.  To  force  such  a  furnace  without  pro- 
ducing smoke  is  an  exceedingly  delicate  operation. 

It  will  be  seen  upon  reference  to  the  drawing,  that  cold  air  is 
at  all  times  in  contact  with  the  boiler  shell,  between  the  points 
"D"  and  "E."  The  strain  upon  the  plates  at  "G"  must  be 
considerable,  owing  to  the  wide  difference  in  temperature  between 
the  points  "E"  and  "F."  There  must  also  be  considerable  loss, 
owing  to  the  cooling  influence  of  the  air  upon  the  exposed  boiler 
shell,  between  "D"  and  "E." 

If  an  even  load  is  carried  and  the  demands  upon  the  boiler 
are  not  excessive,  such  a  device  with  careful  firing  will  give  good 
results  as  to  smokelessness.  Otherwise  there  will  be  constant 
trouble.  With  the  "  down-draft "  furnace,  as  with  most  other 
devices,  a  great  deal  depends  upon  the  assistance  of  the  fireman. 
The  cost  of  this  device,  as  compared  with  many  others,  showing 
equally  good  combustion,  is  excessive. 

A  number  of  furnaces  employ  a  coking  chamber  at  the  sides 
or  front  of  the  fire-box.  The  fresh  coal  is  placed  in  the  chamber, 
which  is  left  open  to  the  air,  the  down-draft  principle  being  utilized. 
The  coal  settles  gradually  as  coking  proceeds,  and  fresh  fuel  is 
supplied  when  required  to  keep  the  contents  of  the  coking  cham- 
ber at  the  proper  level.  The  fireman  must  occasionally  insert 
a  slice  bar  or  other  tool,  and  distribute  the  coked  coal  over  the 
grates.  A  " Dutch  oven"  is  usually  employed  in  conjunction 
with  such  device,  but  some  are  to  be  found  with  coking  chambers 
under  the  boiler  in  the  angle  formed  by  side  walls  and  boiler 
shell.  The  expense  of  any  of  these  contrivances  is  necessarily 
considerable,  and  very  careful  handling  is  required.  If  the 
boiler  is  subject  to  a  fluctuating  load,  difficulty  will  be  experienced 
in  persuading  the  furnace  to  respond  readily  to  the  changing 
conditions. 


CHAPTER  VIII 

SOME    CONCLUSIONS 

The  aim  of  the  author  has  been  to  carefully  point  out  the 
undesirable  features  of  every  type  of  "Smokeless  Furnace" 
likely  to  be  offered  to  the  coal  consumer.  Some  of  the  devices 
on  the  market  combine  the  features  of  several  types,  and  these 
features  must  be  weighed  separately  and  in  combination.  It 
is  indeed  a  poor  device  that  has  no  good  features,  and  it  is  cer- 
tainly a  good  device  if  it  possesses  no  failings.  The  man  who  is 
looking  for  absolute  perfection  in  this  field  will  be  disappointed, 
for  nothing  in  the  furnace  line  can  be  endowed  with  the  factor 
of  intelligence,  and  even  if  so  endowed  it  would  often  have  a 
hard  proposition  to  contend  with,  in  the  ignorance  and  careless- 
ness of  the  men  in  charge  of  the  boiler.  In  selecting  a  device, 
the  purchaser  should  be  guided  by  his  judgment  and  place  very 
little  reliance  upon  the  statements  and  claims  made  by  the 
" smokeless  furnace"  salesman.  He  must  have  sufficient  gen- 
eral knowledge  of  the  requirements  of  combustion,  and  he  must 
take  into  account  the  conditions  obtaining  in  his  own  plant. 
The  fact  that  a  device  is  giving  good  satisfaction  in  his  neighbor's 
plant  cannot  be  taken  as  evidence  that  it  will  give  equally  good 
satisfaction  in  his  own.  What  is  well  adapted  to  one  set  of  con- 
ditions and  circumstances,  may  not  be  at  all  adapted  to  another. 
It  may  be  well  to  cite,  by  way  of  recapitulation,  the  conclusions 
to  be  drawn  from  the  author's  arguments. 

The  conditions  necessary  to  the  combustion  of  the  gases  given 
off  in  the  fire-box  are  as  follows: 

1st.  The  introduction  into  the  fire-box,  and  the  commingling 
with  the  gases,  of  a  sufficient  amount  of  free  oxygen  to  effect 
the  oxidization  of  the  combustible  elements. 

2d.  The  maintenance  of  the  combustible  gases  at  the 
requisite  temperature,  until  combustion  has  been  completed. 

3d.  Sufficient  room  for  the  expansion  of  the  gases  while 
in  the  act  of  combustion. 

96 


SOME  CONCLUSIONS  97 

If  the  above  conditions  are  present,  combustion  will  be  com- 
plete, but  it  must  be  borne  in  mind  that  complete  combustion 
does  not  necessarily  mean  increase  in  efficiency.  It  may  be, 
and  in  the  case  of  most  smokeless  furnaces  is,  accomplished  at 
the  expense  of  efficiency,  owing  to  the  introduction  of  a  redundant 
supply  of  air.  If  fuel  economy  is  desired  the  following  must  be 
provided  for: 

1st.  Regulation  of  the  air  supplied  to  the  fire-box  to  meet 
the  changing  requirements  of  the  gases;  such  regulation,  to  be 
practical,  must  be  accomplished  automatically. 

2d.  The  device  must  be  adjustable  by  experiment  to  meet 
any  combination  of  conditions  offered  by  the  boiler,  grates,  draft, 
etc.,  and  must  be  capable  of  easy  and  quick  readjustment,  to 
meet  any  change  of  conditions  brought  about  by  the  use  of  a 
different  grade  of  coal,  different  method  of  firing,  etc. 

That  device  is  of  course  to  be  preferred  which  both  meets 
the  conditions  necessary  to  complete  combustion  and  is  equipped 
with  means  to  secure  such  combustion  with  the  greatest  economy. 

The  mere  fact  that  a  furnace  is  equipped  with  means  to  auto- 
matically and  adjustably  regulate  the  air  supply,  is  not  in  itself 
sufficient  to  guarantee  that  combustion  of  the  gases  will  take 
place  with  the  greatest  economy.  The  temperature  of  the  air 
introduced,  and  the  manner  of  its  admission  to  the  fire-box,  are 
factors  of  importance.  The  hotter  the  air,  the  less  heat  it  will 
abstract  from  the  burning  gases,  the  more  immediate  and  in- 
timate will  be  the  mixture  of  air  and  gases,  and  the  less  weight 
of  air  will  be  required.  If  the  air  is  diffused  in  a  thin  sheet,  or 
in  a  large  number  of  jets,  across  the  entire  width  of  the  fire-box 
and  above  the  fire,  there  will  be  better  opportunity  for  admixture 
with  the  gases,  and  less  air  will  be  required  to  accomplish  com- 
bustion than  if  admission  is  given  in  some  other  way.  All  other 
things  being  equal,  that  device  is  best  which  introduces  the  air 
at  the  highest  temperature  and  in  such  manner  that  it  will  most 
freely  mingle  with  the  gases  to  be  burned. 

Initial  cost  and  expense  of  maintenance  are  items  to  be  con- 
sidered. Other  matters  being  equal,  these  factors  should  enable 
the  purchaser  to  decide  between  competing  devices.  They  are 
not,  however,  of  primary  importance,  as  a  cheap  device  may 
prove  the  most  expensive  in  the  end. 

Damage  may  result  to  boiler  and  setting  by  the  installation 


98  COMBUSTION  AND  SMOKELESS   FURNACES. 

of  the  factors  necessary  to  a  "smokeless  furnace."  We  will 
briefly  review  the  dangers  to  be  guarded  against,  most  of  which 
have  already  been  pointed  out.  The  purchaser  should  carefully 
inquire  into  the  construction  of  a  device  before  contracting  for 
it,  and  make  sure  that  no  serious  menace  is  offered  either  to  his 
boiler  or  setting.  Following  is  a  partial  list  of  what  may  result 
to  the  boiler  and  setting  by  the  installation  of  various  devices: 

Damage  to  the  boiler  may  result  by 

1st.  Tapping  the  shell  to  connect  water  tubes,  attach  tile 
or  other  elements  in  connection  with  the  device.  Fire  tubes 
are  sometimes  removed  and  pipe  connections  made  at  the  openings. 
It  is  bad  practice  to  interfere  with  the  integrity  of  the  boiler  in 
any  manner. 

2d.  " Bagging"  of  boiler  shell  may  be  caused  by  concen- 
tration of  too  much  heat  at  one  point,  or  the  accumulation  of  too 
much  sediment  at  the  forward  end  of  the  boiler.  Incorrect 
arrangement  of  arches  may  lead  to  this  result,  and  weakening 
of  the  side  walls  may  cause  settling  at  the  forward  end  of  the 
boiler  and  deposit  of  scale  over  the  fire-box. 

3d.  Leaking  a*  the  seams,  due  to  unequal  heating  of  the 
boiler  plates.  Causes  have  been  pointed  out. 

4th.  Formation  of  scale  on  exterior  of  boiler  shell  and  tubes, 
due  to  precipitation  of  carbon  by  "  steam  jets." 

5th.  Pitting  of  boiler  shell  and  tubes,  caused  by  sulphur 
compounds  in  the  scale  deposited  by  "steam  jets." 

Damage  to  boiler  setting  may  result  by 

1st.  Undermining  the  walls  of  the  fire-box,  in  order  to  in- 
stall hollow  tile  or  build  air  conduits  or  chambers. 

2d.  Spreading  of  walls  by  the  lateral  thrust  of  non-self- 
supporting  arches. 

Damage  to  grates  may  result  by 

1st.  Use  of  "  steam  jets,"  the  steam  blown  into  the  fire-box  or 
elsewhere,  posterior  to  the  grates,  displacing  an  equal  volume 
of  air  and  retarding,  to  that  extent,  the  draft  through  the  grates. 

2d.  Introduction  of  surplus  air  above  the  fire,  such  surplus 
air  retarding  the  grates  in  the  same  manner  as  the  "steam  jet." 

3d.     Drawing   air  supply  for  fire-box  from   ash-pit. 

4th.  Oversurplus  of  heat  in  fire-box,  caused  by  superimposed 
arches  and  resulting  in  clinkers  upon  the  grates. 

Damage  to  metal  work  at  front  of  boiler,  may  result  by  over- 
surplus  of  heat  in  fire-box. 


SOME  CONCLUSIONS  99 

Damage  to  efficiency  may  result  by 

1st.     Over-surplus  of  air  supplied  to  gases. 

2d.  Diversion  of  gas  currents  from  boiler  shell,  as  in  the 
case  of  "  retort "  arch  at  rear  of  bridge. 

3d.  Insulation  of  boiler  shell  from  heat  of  furnace,  by  arch 
disposed  over  fire-box. 

4th.  Exposure  of  part  of  the  heating  surface  of  boiler  to 
draft  of  cold  air,  as  in  case  of  device  illustrated  in  Fig.  15. 

All  other  things  being  equal,  that  device  should  be  given 
preference  that  has  no  limitations  as  to  quality  of  coal  or  methods 
of  firing,  and  which  imposes  no  extra  duties  or  hardships  upon 
the  fireman. 

There  are  other  objectionable  features  of  minor  importance, 
peculiar  to  some  furnaces,  but  space  precludes  mention  of  them. 
They  are  usually  so  obvious  as  to  be  apparent  on  examination 
of  the  structural  features  of  the  device. 

If  a  mechanical  stoker  is  to  be  employed,  the  purchaser  must 
select  the  one  best  adapted  to  the  circumstances  of  his  case. 
Preference  might  be  determined  by  the  facilities  provided  for 
regulating  the  feed  of  fuel  and  the  free  air  supplied  to  the  burning 
gases.  Other  things  being  equal,  that  stoker  is  the  best  which 
requires  the  least  care  to  secure  efficient  operation,  and  which 
has  the  fewest  limitations  with  respect  to  character  of  coal. 

With  induced  draft  a  vacuum  is  maintained  in  the  furnace 
and  the  passes  of  the  boiler  and  this  invites  the  entrance  of  out- 
side air  through  every  crack  and  crevice  in  the  setting  where  it 
can  gain  admission.  With  forced  draft  little  or  no  vacuum  is 

THE  "TEST"   DELUSION 

If  the  author  can  succeed  in  discrediting  the  "evaporation 
test,"  as  an  evidence  of  furnace  efficiency,  he  feels  that  he  will 
have  aecomplished  a  service  to  engineering.  Such  tests  may 
be  made  to  prove  anything  desired;  place  no  confidence  in  them. 
The  above  stricture  is  not  intended  to  apply  to  the  evaporation 
test  as  an  evidence  of  boiler  efficiency. 

"Smokeless  furnace  "literature  is  full  of  the  reports  of  evap- 
oration tests,  purporting  to  show  and  prove  increased  efficiency. 
Every  life  insurance  company  claims  superiority  over  every  other, 
and  proves  its  claims  by  an  imposing  array  of  statistics  and 
figures.  There  are  more  opportunities  for  "juggling,"  in  making 


100  COMBUSTION  AND  SMOKELESS   FURNACES 

an  evaporation  test,  than  any  insurance  actuary  has  ever  been 
able  to  discover  in  his  business.  Properly  and  honestly  made, 
the  evaporation  test  is  indicative  of  something  as  to  furnace 
efficiency,  but  the  best  of  such  tests  is  not  conclusive.  If  not 
properly  made,  the  evaporative  test  is  indicative  of  nothing. 
So  many  contingencies  enter  into  the  situation,  that  it  is  even 
possible  for  a  competent  and  experienced  man  to  fool  himself 
in  making  such  a  test.  If  such  test  must  be  made,  and  reliance 
is  to  be  placed  in  it,  it  should  extend  over  sufficient  period  to 
insure  an  averaging  of  conditions,  and  should  be  conducted  by 
parties  in  whom  those  interested  in  the  test  have  the  utmost 
confidence. 

No  less  than  one  hundred  items,  each  one  of  importance, 
must  be  considered  in  running  an  evaporation  test  properly.  If 
one  of  these  items  is  not  taken  into  account,  the  data  is  incom- 
plete. Take,  for  instance,  the  matter  of  atmospheric  conditions. 
The  pressure  of  the  atmosphere,  as  registered  by  the  barometer, 
has  a  bearing  on  the  draft  of  the  chimney.  The  temperature 
of  the  air  applied  to  the  fire  affects  the  temperature  of  combus- 
tion, and  this  has  a  direct  bearing  upon  evaporation.  The  degree 
of  moisture  in  the  atmosphere  also  affects  the  temperature  of 
combustion.  The  coal  used  must  be  carefully  analyzed,  and 
every  wheelbarrow  of  fuel  delivered  to  the  fireman  sampled  for 
this  purpose.  The  resulting  ash  and  clinkers  must  be  weighed 
and  analyzed  before  we  are  able  to  say  what  amount  of  com- 
bustible has  actually  been  used.  We  must  know  the  percentage 
of  moisture  entrained  in  the  steam;  and,  if  such  test  is  to  be  ab- 
solutely accurate,  we  must  know  a  number  of  things  that  are  not 
ascertainable,  and  consequently  never  taken  into  account  in 
conducting  a  test.  For  instance,  the  amount  of  heat  stored  in 
the  walls  of  the  boiler  setting  may  be  sufficient  to  account  for 
several  hundred  pounds  of  coal,  enough  in  a  test  run  of  ten  hours 
to  have  a  bearing  of  several  per  cent,  upon  efficiency.  If  tests 
are  being  conducted  to  determine  the  efficiency  of  a  special  fur- 
nace, and  such  test  is  in  charge  of  a  representative  of  the  device, 
as  is  usually  the  case,  advantage  will  probably  be  taken  of  every- 
thing tending  to  give  the  furnace  the  least  advantage.  If  the 
man  who  is  conducting  the  test  knows  his  business,  the  result 
will  show  a  gain  in  favor  of  the  device,  when,  as  a  matter  of  fact, 
an  actual  loss  might  be  experienced.  It  is  to  the  interest  of  the 


SOME    CONCLUSIONS^'  '161 

device,  that  the  test  made  before  its  installation  be  conducted 
under  as  unfavorable  circumstances  as  possible.  No  effort  will 
be  made  to  clean  the  boiler  shell,  or  stop  air  leaks,  and  no  special 
care  will  be  taken  in  firing.  When  the  device  is  installed,  there 
will  be  a  general  house  cleaning  about  the  boiler.  Scale  will  be 
rubbed  off  the  shell,  and  every  square  foot  of  heating  surface 
made  as  clean  as  possible.  It  will  also  help  some  to  clean  the 
stack  and  breeching,  if  dirty.  All  air  leaks  will  be  stopped,  and 
everything  possible  done  to  put  the  furnace  and  boiler  in  the 
pink  of  condition  for  a  record  performance.  The  test  will  be 
started  with  the  setting  as  hot  as  possible,  and  great  care  will 
be  exercised  in  firing.  Such  precautions  alone  are  good  for  a 
showing  of  from  ten  to  twenty  per  cent,  improvement  in  efficiency. 
Those  best  acquainted  with  the  evaporation  test  place  the  least 
confidence  in  it. 

The  proper  test  to  apply  to  any  device  claiming  to  improve 
combustion  is  a  flue  gas  analysis.  Such  analysis  not  only  de- 
termines the  extent  of  the  combustion  but  the  percentage  of 
surplus  air  carried  with  the  chimney  gases.  If  combustion  is 
at  the  maximum,  and  surplus  air  at  the  minimum,  the  highest 
efficiency  possible  is  attained.  The  amount  of  water  evaporated 
per  pound  of  coal,  the  quality  of  the  steam  and  every  other  item 
that  must  be  noted  in  connection  with  an  evaporation  test,  may 
be  disregarded.  The  evaporation  test  is  necessary  to  determine 
boiler  efficiency,  but  should  not  be  employed  to  determine  any- 
thing related  to  combustion. 


•     APPENDIX. 

This  volume  would  be  incomplete  without  an  appendix 
describing  the  combustion  testing  apparatus  most  commonly 
employed  in  working  out  smoke  problems  and  improving  the 
efficiency  of  furnace  and  boiler.  The  author  ventures  to  illus- 
trate certain  apparatus  designed  by  himself  and  in  doing  this 
he  must  not  be  considered  as  disparaging  any  apparatus  that 
may  have  been  designed  by  others.  Something  should  also  be 
said  about  soot,  because  soot  deposits  constitute  one  of  the  most 
expensive  results  of  incomplete  combustion. 

As  pointed  out  in  the  preceding  pages  smokeless  combustion 
depends  upon  proper  furnace  design  and  proper  fuel  and  air 
supply.  If  there  is  lack  of  air,  lack  of  temperature,  lack  of 
mixture  between  the  air  and  the  gases  or  lack  of  space,  there 
will  be  smoke.  The  smoke  from  your  furnaces  may  be  due 
to  one  of  these  causes.  It  may  result  from  a  combination  of 
two  or  more  of  them.  You  cannot  provide  a  proper  remedy  for 
the  smoke  until  you  know  absolutely  what  the  causes  of  the 
smoke  may  be.  You  may  waste  a  great  deal  of  money  if  you 
buy  smokeless  furnaces  and  automatic  stokers  on  the  representa- 
tions of  the  salesmen  alone.  Most  of  these  salesmen  can  point 
to  satisfactory  results  that  have  been  attained  in  other  plants. 
But  you  must  remember  that  the  other  plants  are  not  your 
plants  and  that  a  remedy  exactly  adapted  to  the  smoke  trouble 
in  one  boiler  room  may  fail  absolutely  to  meet  the  situation  in 
another.  Your  particular  case  must  be  "diagnosed"  before 
the  contract  is  placed  for  the  furnace  or  stoker. 

And  you  must  remember,  as  the  author  has  been  at  pains 
to  point  out,  that  a  smokeless  furnace  is  not  necessarily  an  eco- 
nomical furnace.  In  this  connection  the  reader  may  again  refer 
to  the  discussion  relating  to  the  diagram,  Figure  2,  preceding. 

It  is  easy  to  determine  whether  there  is  sufficient  tempera- 
ture for  combustion.  Mere  observation  of  the  fire  will  be  suffi- 

103 


104 


COMBUSTION  AND  SMOKELESS  FURNACES 


cient.  If  the  furnace  is  white  hot,  the  smoke  is  not  due  to  lack 
of  temperature.  It  is  not  so  easy  to  determine  which  of  the 
other  three  causes  mentioned  may  be  responsible  for  the  smoke. 
If  the  furnace  dimensions  are  known,  together  with  the  areas  of 
the  various  boiler  passes,  etc.,  we  may  make  a  fair  guess  regard- 
ing the  matter  of  space,  but  it  would  be  a  guess,  and  guesses 
are  often  wrong.  The  space  required  depends  upon  the  flam- 
ing characteristics  of  the  coal.  "What  would  be  ample  space  for 
one  fuel  might  be  very  inadequate  for  another.  We  may  pro- 
ceed with  certainty  in  diagnosing  combustion  problems,  only 
when  we  are  equipped  with  proper  combustion  testing  appa- 
ratus. 


ILLUSTRATION  SHOWING  THE  "OBSAT"  PRINCIPLE 
OF  GAS  ANALYSIS. 


The  gas  to  be  analyzed  is 
taken  into  the  "  burette" 
"B,"  the  cock  "Bl"  being 
opened  for  the  purpose.  The 
" Leveling  Bottle"  "L"  is 
filled  with  water.  "L"  is 
then  raised  with  the  hand  and 
water  flows  from  it  through 
the  connecting  rubber  tube 
into  ' '  B, "  ' '  seeking  its  level. ' ' 
"Bl"  is  closed  when  the 
water  reaches  the  zero  mark 
on  the  scale  etched  on  "B." 
The  water  levels  in  "B"  and 
"L"  should  then  be  in  the 
same  horizontal  plane,  thus 
giving  a  measurement  at  at- 
mospheric pressure  of  the  ex- 
act gas  sample  called  for  by 
the  "burette." 


Engineer's  Gas  Ana- 
lyzer— a  modified 
form  of  "Orsat"  de- 
signed by  the  author. 


APPENDIX 


105 


"A"  is  charged  with  a  gas  absorb- 
ing liquid.  The  cock  "Al"  is  opened 
and  "L"  raised,  the  water  driving  the 
gas  from  ' '  B  "  into  ' '  A, "  displacing  the 
liquid  in  the  latter.  The  C02  contained 
in  the  gas  is  absorbed  by  the  liquid  and 
this  causes  a  contraction  in  the  gas 
sample.  The  gas  remaining  is  then 
pulled  back  into  "B"  by  lowering  the 
Leveling  Bottle.  The  chemical  (Caus- 
tic Potash  solution)  must  be  drawn  up 
into  the  capillary  tube  at  the  top  of 
"A"  before  the  cock  "Al"  is  closed. 

The  bottle  "L"  is  then  held  in  such 
position  that  the  surface  of  the  water  is 
in  the  same  horizontal  plane  as  that  of 
the  water  in  "B."  This  places  the  gas 
under  atmospheric  pressure  and  the 
reading  is  taken. 
Additional  absorber  pipettes,  similar  to  "A,"  are  connected 

by  a  manifold  with  "B"  and  charged  with  the  proper  solutions 

if  Oxygen  and  CO  are  to  be  determined. 


THE  GAS  ANALYZER  APPLIED  TO  SMOKE  PROBLEMS. 

It  may  be  quickly  determined  with  the  Gas  Analyzer  whether 
the  air  supply  is  sufficient  or  insufficient.  If  the  escaping  fur- 
nace gases  contain  5  or  6  per  cent  free  Oxygen,  there  is  ample 
air  for  complete  combustion  and  the  smoke  must  be  charged 
to  one  or  more  of  the  three  remaining  causes.  The  question  of 
temperature,  as  already  stated,  may  be  settled  by  observation  of 
the  fire  in  the  furnace,  and  if  the  temperature  required  is 
actually  present  we  will  know  that  the  smoke  is  caused  by 
lack  of  mixture  or  lack  of  space. 

If,  on  further  examination  of  the  gases  of  combustion,  CO 
(Carbon  Monoxide)  is  present,  a  strong  presumption  arises  that 
the  smoke  is  due  to  lack  of  mixture,  because  free  Oxygen  and 
combustible  gas  cannot  exist  together  in  the  presence  of  an  ignit- 
ing temperature.  If,  however,  the  Carbon  Monoxide  is  produced 


106  COMBUSTION  AND  SMOKELESS  FURNACES 

in  one  part  of  the  furnace  and  the  excess,  or  unused  oxygen,  rises 
through  the  grate  into  another  portion  of  the  furnace,  the  two 
may  not  come  into  contact  until  the  furnace  and  the  various 
passes  of  the  boiler  have  been  traversed,  when  the  temperature 
may  be  too  low  to  promote  ignition. 

A  better  mixture  can  usually  be  promoted  by  more  skillful 
firing.  The  fuel  upon  the  grate  should  at  all  times  be  kept  in 
such  condition  that  there  will  be  a  uniform  distribution  of  air 
through  the  fuel  bed.  Such  distribution  is  possible,  only  when 
the  fuel  bed  is  of  uniform  resistance,  viz.,  of  uniform  thickness, 
free  from  holes  and  fissures  and  the  grate  free  everywhere  from 
ash  accumulations.  If  the  fuel  bed  is  thick  in  some  places  and 
thin  in  others,  and  especially  if  the  grates  are  bare  in  places  or 
if  there  are  holes  or  fissures  in  the  "fire"  the  air  distribution 
will  be  very  uneven.  Where  the  fuel  is  excessively  thick,  CO 
will  be  formed. 

If  satisfactory  mixture  cannot  be  secured  by  equalizing  the 
air  distribution  through  an  improved  firing  practice,  the  engi- 
neer of  the  plant  may  be  forced  to  resort  to  some  of  the  expedi- 
ents described  in  the  body  of  this  book,  viz.,  mixing  or  baffling 
arches,  piers,  etc. 

There  may  be  dense  black  smoke  in  the  absence  of  combustible 
Carbon  Monoxide,  in  which  case  it  is  reasonably  safe  to  conclude 
that  the  prime  cause  is  lack  of  space.  When  the  burning  gases 
come  into  contact  with  the  cold  heating  surfaces  of  the  boiler, 
carbon  is  precipitated  as  soot.  When  smoke  is  caused  in  this 
manner,  it  may  be  very  black  and  dense  and  there  may  be  no 
trace  of  Carbon  Monoxide  present.  If  smoke  is  caused  by  lack 
of  mixture,  some  measure  of  Carbon  Monoxide  is  almost  certain 
to  be  found  in  the  gases. 

The  author  has  tried  to  show  that  a  clean  chimney  does  not 
necessarily  indicate  efficient  combustion,  for  it  is  indisputable 
that  combustion  may  be  complete  at  furnace  temperatures  much 
lower  than  those  called  for  by  good  practice, — the  lowered  tem- 
peratures being  caused  by  the  introduction  of  a  large  excess  of 
air  through  the  fuel  bed. 

More  fuel  waste  is  caused  by  excess  air  than  by  all  other 
agencies  combined  and  a  redundant  supply  of  air  usually  con- 
tributes to  the  completeness  of  combustion  by  improving  mix- 


APPENDIX  107 

ture.  Hence  it  is  possible  for  a  steam  plant  to  experience  a  de- 
crease in  smoke  with  an  attendant  decrease  in  efficiency.  These 
things  are  not  generally  understood.  Smokeless  combustion  is 
not  necessarily  economical  combustion. 

All  combustion  problems,  however  obscure  or  complicated  they 
may  be,  are  quickly  cleared  up  by  means  of  the  Gas  Analyzer. 
In  ordinary  boiler  furnace  practice  it  is  not  often  necessary  to 
go  further  than  the  determination  of  C02.  Knowing  the  per- 
centage of  Carbon  Dioxide,  we  know  approximately  the  percent, 
age  of  free  Oxygen  (excess  air)  in  the  flue  gases.  The  following 
formula  may  be  used  in  computing  the  air  excess  from  the  C02 : 
20.7 — C02  percentage 

XlOO=Excess  air. 

C02  percentage 

In  the  following  table  the  air  excess  corresponding  to  per- 
centages of  C02  from  1  to  20.7,  inclusive,  is  shown : 

Per  cent  C02,  Per  cent  Air  Excess. 

1  1,970 

2  935 

3  590 

4  417 

5  314 

6  245 

7  195.7 

8  158.7 

9  130 

10  107 

11  88.1 

12  72.5 

13  59.2 

14  47.8 

15  38 

16  29.4 

17  21,79 

18  15 

19  8.95 

20  0.035 
20.7  0.000 


108  COMBUSTION  AND  SMOKELESS  FURNACES 

At  about  1.5  per  cent  C02,  the  cooling  effect  of  the  excess  air 
in  the  furnace  gases  is  so  great  that  the  efficiency  of  the  furnace 
and  boiler  as  steam  generators  would  be  zero. 

Boiler  plants  that  are  operated  without  combustion  super- 
vision show  upon  the  average  about  6  per  cent  C02,  while  it 
would  be  easy  in  nearly  every  case  by  a  little  attention  to  the 
air  leaks  common  in  brick  boiler  settings  and  a  little  study  of 
drafts  and  methods  of  firing  to  increase  the  percentage  to  14  or 
15,  thereby  reducing  the  air  excess  from  about  245  to  around  40. 
This  would  mean  a  reduction  in  fuel  consumption  of  about  17 
per  cent. 

Draft  is  an  extremely  vital  factor  in  furnace  efficiency.  There 
is  some  draft  that  will  produce  the  best  results  and  the  engineer 
in  charge  of  the  plant  must  ascertain  what  his  standard  draft  for 
normal  working  conditions  may  be.  Having  learned  this  he 
must  see  that  such  draft  is  applied  to  all  of  his  furnaces  all  of 
the  time,  as  far  as  may  be  practicable.  Change  in  load  may 
require  change  in  draft,  but  the  standard  working  draft  should 
be  adhered  to  as  much  as  possible. 

A  differential  draft  gage  properly  connected  at  the  furnace  is 
of  great  assistance  to  the  fireman  in  maintaining  efficiency.  If 
there  really  is,  as  already  stated,  some  draft  that  will  produce 
the  best  economy  in  the  consumption  of  coal,  the  fireman  can- 
not be  held  to  the  use  of  that  draft  unless  he  is  provided  with 
gages  showing  the  draft.  He  must  be  instructed  what  draft  to 
use.  Each  boiler  is  provided  with  a  water  gage  in  order  that  the 
fireman  may  know  at  all  times  the  stage  of  the  water  in  the 
boiler.  A  draft  gage  for  each  boiler  furnace  is  necessary  in 
order  that  the  fireman  may  know  at  all  times  the  state  of  the 
draft  in  the  boiler  furnace.  And  as  the  fireman  is  taught  to 
vary  the  water  level  in  the  boiler  within  certain  limits  in  order 
that  the  boiler  may  accommodate  itself  to  fluctuations  in  the 
load,  he  may  also  be  taught  to  vary  the  drafts  within  certain 
limits  that  the  furnace  may  easily  respond  to  like  fluctuations 
in  load. 

The  fireman  soon  learns  to  employ  the  draft  g age  as  an  indi- 
cator of  conditions  inside  the  furnace.  A  decreasing  draft  indi- 
cates that  holes  are  forming  in  the  fuel  bed  or  that  the  fuel  is 


APPENDIX  109 

being  reduced  in  thickness  and  an  increasing  draft  shows  that 
the  fuel  bed  is  too  thick  or  that  the  fires  are  getting  ' '  dirty. ' ' 

Air  leaks  are  the  most  common  causes  of  draft  interference. 
These  may  occur  at  any  place  between  the  furnace  and  the  top 
of  the  chimney.  The  function  of  the  chimney  is  to  create  a  par- 
tial vacuum  inside  the  furnace,  and  as  a  result  of  the  difference 
in  pressures,  air  flows  into  the  furnace  through  the  fuel  and  the 
necessary  oxygen  is  supplied  to  the  combustible.  Any  opening 
between  the  furnace  and  the  top  of  the  chimney  will  admit  air, 
thereby  "  breaking "  the  vacuum  and  impairing  the  draft.  Seri- 
ous air  leaks  are  common  at  the  places  where  the  breeching  con- 
nects with  the  chimney  and  with  the  boiler.  These  leaks  impair 
draft,  but  they  do  not  necessarily  impair  combustion  efficiency. 
Air  leaks  are  extremely  common  about  boiler  settings — especially 


Type  of  Differential  Draft  Gage  designed  by  the  Author. 

about  the  settings  of  water  tube  boilers.  Such  leaks  admit  air  to 
the  heating  surfaces  of  the  boiler  and  impair  both  draft  and 
efficiency. 

There  is  but  one  rule  of  general  application  regarding  draft, 
and  the  term  " draft"  as  here  used  must  be  understood  to  mean 
the  vacuum  in  the  furnace  over  the  fire. — * '  That  draft  which  will 
produce  the  highest  percentage  of  C02,  without  CO,  and  which 
will  carry  the  load,  will  produce  the  highest  economy  in  fuel 
consumption. ' ' 

The  above  being  true,  it  is  necessary  to  know  something 
about  the  constitution  of  tie  flue  gases  before  fixing  upon  the 

*For  a  discussion  of  efficient  combustion,  see  "How  to  Build  Up  Fur- 
nace Efficiency,"  by  the  Author. 


110 


COMBUSTION  AND  SMOKELESS  FURNACES 


standard  draft  for  the  plant.  When  the  standard  draft  is  known 
it  remains  to  apply  this  draft  to  all  furnaces  by  adjusting  the 
individual  boiler  dampers  and  to  maintain  this  draft  at  all  times 
so  far  as  the  fluctuations  in  the  load  will  permit.  All  authorities 


Automatic  Gas  Sampler  and 
Combined  CO2  and  Draft  Re- 
corder designed  by  the  Author 


seem  agreed  upon  the  proposition  that  the  Gas  Analyzer  pro- 
vides the  only  certain  means  of  determining  the  draft  to  be  used. 
Let  us  assume  that  the  draft  selected  as  the  standard  for  the 
plant  is  thirty-hundredths  of  an  inch  over  the  fire  and  that  the 


APPENDIX  111 

use  of  such  draft  together  with  skillful  firing  will  produce  an 
average  of  14  per  cent  C02  in  the  chimney  gases.  It  remains  to 
make  certain  whether  the  firemen  are  employing  the  proper  draft 
and  observing  all  the  instructions  that  may  have  been  given  them 
regarding  firing  or  the  operation  of  the  stokers.  To  this  end  an 
automatic  C02  Recorder  or  an  Automatic  Gas  Collector  may  be 
employed.  The  Recorder  produces  records  upon  a  chart  at  inter- 
vals of  a  minute  or  more  as  desired,  showing  the  percentages  of 
C02  in  the  flue  gases.  The  Gas  Collector  traps  a  quantity  of  the 
flue  gases  drawn  at  a  uniform  rate  over  any  desired  period,  as 
for  example  a  firing  watch,  and  at  the  end  of  the  period  the 
trapped  gas  is  analyzed  and  the  percentages  of  C02,  Oxygen 
and  CO  are  determined.  The  illustrations  show  the  C02  Re- 
corder and  the  Gas  Collector  designed  by  the  author. 

The  subject  of  combustion  cannot  be  dismissed  without  a  con- 
sideration of  soot.  Soot  is  inevitable  wherever  a  carbonaceous 
fuel  is  burned  and  practically  all  fuels  are  based  on  carbon.  The 
better  the  combustion  the  less  soot  there  will  be.  But  no  matter 
how  ideal  the  combustion  conditions  may  be,  soot  will  be  formed 
at  certain  stages,  as  for  example  when  fresh  fires  are  being 
started,  and  it  requires  but  a  thin  coating  of  soot  upon  the  heat- 
ing surfaces  of  the  boiler  to  seriously  retard  the  transfer  of  heat 
to  the  water.  A  pound  of  carbon  reduced  to  the  form  of  soot 
and  distributed  upon  the  heating  surfaces  of  a  boiler  will  inter- 
fere in  a  very  marked  degree  with  the  efficiency  of  the  boiler  as 
a  heat  absorber. 

The  non-conducting  properties  of  carbon,  and  especially  of 
carbon  in  the  form  of  soot,  are  not  generally  understood.  An 
idea  of  the  relative  conducting  properties  of  steel  and  carbon 
may  be  obtained  by  taking  a  charcoal  pencil  in  one  hand  and  a 
steel  bolt  in  the  other  and  then  holding  the  ends  of  the  two  in 
the  flame  of  a  Bunsen  burner.  The  bolt  will  be  too  hot  to  hold 
in  a  few  moments,  while  the  charcoal  pencil  may  be  held  indefi- 
nitely. 

It  has  been  determined  that  one  square  foot  of  steam  pipe  at 
a  temperature  of  310  deg.  F.  will  transmit  heat  units  through 
various  coverings  one  inch  thick  as  follows : 


112  COMBUSTION  AND  SMOKELESS  FURNACES 

B.  t.  u.  per  sq.  ft. 
Covering.  per  minute. 

Fine  Asbestos 8.17 

Loose  Anthracite  Coal  Ashes 4.50 

Asbestos  Paper  (wound  tight) 3.62 

Cork  Strips  (bound  on) 2.43 

Paper 2.33 

White  Pine  Charcoal 2.32 

Cork  Charcoal  1.98 

Compressed  Lampblack 1.77 

Loose  Lampblack  (soot) 1.63 

From  this  table  it  appears  that  soot  will  resist  the  transfer- 
ence of  heat  five  times  as  effectively  as  fine  asbestos  and  we  are 
struck  by  the  fact  that  a  coating  of  soot  one-tenth  of  an  inch 
thick  on  the  boiler  surfaces  will  interfere  as  seriously  with  that 
boiler  as  a  coating  of  fine  asbestos  one-half  inch  thick.  It  will 
also  be  observed  from  the  table  given,  that  loose  anthracite  coal 
ashes  make  an  insulating  covering  almost  twice  as  effective  as 
asbestos.  Incidentally  the  table  shows  why  cork  as  an  insulating 
material  is  coming  so  rapidly  to  the  front  in  popular  favor. 

Deposits  of  soot  upon  the  boiler  to  some  extent  are  inevitable, 
no  matter  what  the  fuel.  They  will  even  occur  where  gas  is 
burned.  Deposits  of  ash,  especially  where  high  ash  bituminous 
coals  and  steam  grades  of  anthracite  are  burned,  may  be  quite  as 
troublesome  as  soot.  Good  practice  demands  the  employment  of 
proper  equipment  to  keep  the  boilers  clean  of  soot  and  ash  accu- 
mulations. 

Soot  is  always  an  evidence  of  improper  combustion  and  there 
is  always  a  time  when  the  best  designed  furnace  will  suffer  from 
improper  combustion  and  produce  some  smoke  and  some  soot. 
Again  the  best  designed  furnace  may  deposit  ash  all  of  the  time. 
Hence  it  is  quite  imperative  when  designing  a  boiler  plant  to 
make  proper  provision  for  the  frequent  and  thorough  cleaning  of 
the  tubes  and  other  heating  surfaces. 

The  author  is  disposed  to  question  the  thoroughness  of  what 
have  come  to  be  known  as  "hand  blowers/'  because  it  is  quite 
impossible  to  bring  such  blowers  to  bear  upon  all  of  the  heating 
surfaces  and  impossible  again  to  so  direct  the  steam  jets  from  a 


APPENDIX 


113 


hand  blower  that  the  soot  will  be  effectively  driven  away  from 
the  parts  actually  "cleaned."  The  illustrations  show  approved 
and  very  effective  permanent  soot  blowers  as  arranged  for  Stir- 
ling and  B.  and  W.  types  of  boilers.  With  such  an  installation 
it  is  possible  to  effectively  sweep  every  square  inch  of  the  heating 
surfaces  and  to  blow  the  passes  of  the  boiler  progressively, 
thereby  forcing  all  of  the  soot  from  the  boiler  to  the  chimney. 


Showing  Permanent  Installation  of  Soot  Cleaners  on  Stirling 
and  B.  &  W.  Type  of  Boiler. 

The  author  will  leave  the  question  of  soot  removal  by  quoting 
from  an  article  in  the  March  10,  1914,  issue  of  "  Power"  written 
by  Chas.  Bromley,  one  of  the  editors  of  that  magazine. 

"An  engineer  with  an  eye  for  economy  looks  carefully  after 
his  boiler  setting  so  as  to  reduce  the  air  leakage  to  a  minimum. 
The  practice  of  encasing  the  whole  setting  in  steel  is  excellent  and 


114  COMBUSTION  AND  SMOKELESS  FURNACES 

is  increasing,  but  engineers  realize  that  there  is  a  greater  gain 
if  the  blow  doors  are  also  encased,  as  it  is  practically  impossible 
to  keep  these  doors  air-tight.  To  overcome  this  difficulty,  it  has 
become  common  practice  to  omit  the  dusting  doors  and  steel  case 
the  entire  setting,  and  install  some  type  of  mechanical  soot  blower 
for  cleaning  the  boiler  tubes. 

One  of  the  largest  New  York  companies  recently  installed 
thirty-two  600-horsepower  horizontal  water-tube  boilers,  14  tubes 
high  by  21  tubes  wide.  These  boilers  are  steel  cased  with  no  pro- 
vision for  hand  cleaning.  The  boilers  are  cleaned  by  means  of  a 
mechanical  soot-blowing  system,  consisting  of  eight  2-inch  blow 
pipes,  which  extend  across  the  width  of  the  boilers.  Four  of  these 
pipes  are  at  the  top  of  the  first  pass,  two  at  the  top  of  the  second 
pass  and  two  at  the  top  of  the  third  pass.  Each  pipe  is  equipped 
with  special  three-way  nozzles  drilled  so  as  to  project  the  steam 
obliquely  between  the  tubes.  The  nozzles  on  alternate  blow  pipes 
project  the  steam  down  through  the  space  between  the  tubes  on 
intersecting  planes  and  between  different  pairs  of  tubes,  so  that 
the  steam  cross-fires  over  the  heating  surface.  An  additional 
2-inch  pipe  with  smaller  branch  blow  pipes  cleans  the  super- 
heater. 

In  the  article  under  discussion  the  statement  is  made  that  the 
worst  feature  of  all  forms  of  fixed-jet  apparatus  is  that  they 
cannot  be  spaced  close  enough  to  effectively  clean  the  tubes. 
This  statement  seems  hardly  in  keeping  with  the  evidence  at 
hand.  The  foregoing  tests  indicate  that  the  soot  blowers  reach 
considerable  soot  that  is  inaccessible  to  hand  blowing.  • 

Many  of  the  most  progressive  power  plants  in  the  country, 
especially  in  the  electric-light  and  railway  field,  have  been  using 
mechanical  soot  cleaners  for  years  and  have  placed  repeat  orders 
until  every  boiler  is  equipped  with  such  blowers,  which  is  evi- 
dence that  the  cleaners  must  be  real  soot  removers. 

The  fact  that  users  of  the  latest  improved  soot-blowing  sys- 
tems do  not  go  within  the  settings  to  remove  soot  by  hand  would 
further  indicate  that  such  blowing  systems  are  efficient.  In  the 
case  of  hand  blowing,  however,  it  is  always  necessary  to  resort 
to  such  periodic  cleanings. 

One  of  the  main  troubles  experienced  in  trying  to  blow  soot 
from  boiler  tubes  by  a  hand  steam  lance  is  the  impossibility  of 


APPENDIX  115 

using  one  long  enough  to  reach  across  the  boiler.  This  results 
in  the  soot  piling  up  on  the  tubes  at  the  far  side  of  the  boiler. 
With  the  boilers  set  in  batteries,  as  is  the  usual  practice,  it  is  im- 
possible to  overcome  this  difficulty  when  blowing  the  tubes  by 
hand.  Even  where  it  is  possible  to  use  a  lance  across  the  boiler 
width,  this  blowing  does  not  clean  the  sides  of  the  tubes,  which 
play  an  important  part  in  the  evaporation  of  water. 

The  soot  clings  to  the  tube  side,  defying  removal  by  hand 
blowing,  and  the  soot  on  the  tops  of  the  tubes  at  either  side  of  the 
blow  doors  remains  untouched.  The  bulk  of  the  soot  that  is 
reached  by  the  hand  blowing  is  really  not  all  removed,  but  is 
stirred  up  and  a  portion  settles  on  the  tubes  again.  Cleaning  the 
top  of  a  tube  prevents  some  waste,  but  a  properly  designed  soot 
cleaner  cleans  the  whole  tube  surface  and  is  much  more  efficient. 

To  further  illustrate  the  losses  occasioned  by  soot  on  boiler 
tubes  the  results  obtained  at  one  of  the  largest  electric  plants  in 
the  country  are  as  follows :  Starting  with  a  clean  600-horsepower 
horizontal  water-tube  boiler  at  50  per  cent  over  rating,  the  gas 
temperatures  in  the  uptake  were : 

Degrees 

First  day 550 

Second  day 575 

Third  day 600 

Fourth  day 625 

Fifth  day 650 

These  boilers  had  no  blowing  system,  and  in  fact  were  not 
even  blown  by  hand,  and  the  increase  in  uptake  temperature  is 
significant. 

Another  test  which  emphasizes  even  more  strongly  the  im- 
portance soot  plays  in  relation  to  boiler  efficiency,  and  also  illus- 
trates the  efficiency  of  the  mechanical  soot  blower  employed,  was 
conducted  by  recognized  engineers  at  one  of  the  largest  electric- 
lighting  plants  in  the  Middle  West. 

On  a  new  750-horsepower,  water-tube  boiler,  never  before 
fired,  the  tubes  were  blown  at  the  end  of  the  first  hour 's  run  and 
immediately  there  was  a  drop  of  20  per  cent  in  the  uptake  tem- 
perature. Twelve  hours  later  the  tubes  were  again  blown  and  a 
drop  in  the  uptake  temperature  of  between  65  and  70  deg.  took 


116 


COMBUSTION  AND  SMOKELESS  FURNACES 


place.  These  figures  show  the  effect  that  soot  has  on  boiler  effi- 
ciency and  also  show  the  importance  of  frequent  and  thorough 
cleaning. 

It  is  stated  that  with  good  firing  a  reduction  of  50  deg.  F. 
in  the  flue  temperature  will  mean  a  saving  of  3  per  cent  in  the 
coal  bill.  In  connection  with  this  statement,  which  is  acknowl- 
edged to  be  approximately  correct,  it  will  be  interesting  to  study 
the  accompanying  chart,  which  was  taken  at  one  of  the  largest 
cotton  mills  in  Massachusetts. 

During  the  afternoon  of  the  day  of  the  test,  experiments  were 
being  made  with  a  new  grade  of  coal  and  new  methods  of  firing, 
in  consequence  of  which  the  readings  of  temperature  during  the 
afternoon  were  erratic.  However,  accepting  the  average  as 
shown  by  this  chart,  it  will  be  seen  that  the  soot-blowing  device, 
while  not  receiving  all  credit  due  it,  still  shows  marked  economy. 
On  the  boiler  equipped  with  the  mechanical  soot  blower  the  chart 
shows  an  average  reduction  in  uptake  temperature  of  77  deg.  F. 
in  comparison  with  the  boiler  cleaned  by  hand.  This  77  deg.  F. 
reduction  represents  a  4.6  per  cent  saving  in  fuel. 

Mechanical  soot  blowers  have  been  in  process  of  development 
for  the  past  10  or  12  years,  during  which  time  much  valuable 
experience  has  naturally  been  gained  by  the  pioneers  in  this  field. 
Soot  cleaners  installed  without  the  proper  experience  or  design 
back  of  them  can  hardly  be  expected  to  give  the  best  results. 

Most  engineers  admit  that  soot  defies  removal  by  hand  blow- 
ing. It  is  generally  admitted  that  the  mechanical  soot  blower 
correctly  designed,  properly  installed  and  intelligently  operated 
is  the  real  solution  to  the  soot  problem. ' ' 


ye rage 


Chart  of  Temperatures  of  Flue  Gases,    With    Hand  and    Cleaner   Blown 

Tubes. 


INDEX 


PAGE 

Air  —  admission    into    furnace    through 

arches 84 

through  bridge  wall 82 

through  fire-doors 79 

through  grates 78 

through  side  walls 80 

Composition  of 14 

Distribution  of— problems  concerning. .  26 
Excess  of— may  increase  stack  temper- 
ature    59 

Expansion  of 29 

Inlets  into  furnace — 

location  and  shape  of. .  28 

Inlets  into  furnace— size  of 27 

Introduction    into    furnace  —  problems 

connected  with 26 

Introduction  above  the  ftre 28 

Regulation 29 

Regulation — experiments  in 59 

Regulation— ideal  method  of 31 

Regulation — necessity  of , 26 

Regulation — should  be  automatic. 69 

Regulation — statements  of  authorities, 

32,  33»  34 

Temperature  of  furnace  fed 29 

Baltimore  thermal  unit 1 

Bertholet's  second  law 16 

Boiler — combustion  and  the 36 

Cornish 38 

Economies 52 

Evolution  of 37 

Lancashire 38 

Marine 38 

Requisites  of 36 

Wagon 37 

Water-tube — two  general  classes 38 

British  thermal  unit 7 

Calory 8 

Carbonic  acid  gas,  in  air  of  cities 48 

Carbon  dioxide 14 

Percentage   of,    as    index    of    furnace 

efficienc  y 24 

Carbon  monoxide 15 

Air  required  to  burn 26 

Loss  due  to 16 

Poisonous 43 

Carbureted  hydrogen I!) 

Chain  grates 62 


PAGE 

Chicago  coal  receipts  and  shipments 52 

Chimney  evil,  the 41 

A  menace  to  health 42 

Chimney  gases— poisonous 42 

Chimneys — low  ones  menace  to  health  ....  43 

Coals— composition  of 19 

Coal  consumption  in  Chicago 51,  52 

Coal — elements  of 19 

Coal  gases  vs.  coke  gases 19 

Combustible — requisites  of 12 

Combustion 1 

In  the  boiler  furnace. 12 

Experiments  touching 18 

Primary  requisites  of 25 

Retarded  by  cold  surfaces 17 

Requisites  of 18 

Two  operations  contemplated  by 12 

Cornish  boiler 33 

Down-draft  furnaces 93 

Draft — acceleration  by  steam  jets 68 

Explanation  of < 14 

Dutch  oven  furnaces 39,  92 

Energy— actual 5 

Definition  of 5 

Of  position 5 

Potential 5 

Evaporation  tests— delusions  concerning  . .  99 

Evelyn  on  Smoke 49 

Fire-arch  furnaces 85 

Fireman's  services  underrated 53 

Firemen — how  Germany  treats  them 64 

Flame — cause  and  appearance  of 22 

Temperature  of 23 

Flue  gases— analysis  of 23,  24 

Fooling  the  smoke  inspector 44 

Force — definition  of 6 

French  thermal  unit 8 

Fuel— proper  selection  of,  important 63 

Fuel  spreaders 65 

Furnaces — down-draft 93 

Dutch  oven 39,  92 

Efficiency  of,  formula  for  computing  . .  37 

Fire-arch 85 

Gases  from— heat  values  of 22 

Hand-fired 67 

Natural  draft 69 

Smokeless 56 


117 


PAGE 

Furnaces- 
Smokeless— classification  of 60 

Smokeless — early  forms  of 57 

Smokeless— not  always  what  they  seem.  44 

Smokeless— requisites  of 68 

Smokeless— patents  numerous 68 

Smokeless— points  to  be  avoided 98 

Gas — marsh 21 

Olefiant 21 

Gas  works — products  of 21 

Gases— chilling  of  combustible 17 

Coal  vs.  coke 19 

Flue— analysis  of 23,  24 

Indicating  complete  combustion 25 

Indicating  incomplete  combustion 25 

Furnace — air  required  to  burn 27 

Furnace — heat  values  of 22 

Grates— chain 62 

Inclined 64 

Heat— definitions  of 3 

Kinetic  theory  of 2 

Latent 8 

Latent— illustrations  of 8,  9,  10 

Material  theory  of 2 

Mechanical  equivalent  of 5 

Performance  of  in  the  cylinder 11 

Sensible 8 

Specific 8 

Theories  «f 1 

Heat  energy— absolute  zero  of 4 

Heat  and  combustion 1 

Heat  vs.  temperature 3 

Hydro-carbons 1» 

Hydrogen— carbureted 19 

Inclined  grate  stokers 64 

Inlets,  air— location  and  shape  of 28 

Air,  sizes  of 27 

Jets— steam 45 

Cost  of  operating 71 

General  discussion  of 70 

Increase  carbon  monoxide 46 

Increase  sulphuric  acid  vapors 47 

Objections  to 71 

Reactive  in  effect  upon  combustion  ...  46 

Joule — experiments  of 6 

Lancashire  boiler 38 

London's  smoke  troubles 50 


PAQK 

Mechanical  draft 67 

Mechanical  stokers 61 

General  observations  on 66 

Mechanical  equivalent  of  heat 5 

Natural  draft  furnaces 69 

.  21 


Olefiant  gas 

Overfeed  stokers. 


Marine  boiler . 
Marsh  gas  ... 


21 


Potential  energy 5 

Pulverized  fuel  burners 65 

Rowland— experiments  of 65 

Smoke— kills  vegetation 50 

Smoke  abatement — early  history  of 51 

Smoke  burning — disagreement  of  authori- 
ties as  to  use  of  term 56 

Is  the  term  proper  ? 56 

Parlor  experiments  in 57 

Smoke  nuisance  vs.  chimney  evil 41 

In  Chicago  —  early   history   of   propa- 
ganda against 51 

Smoke  ordinances — overlook  chimney  evil.  41 

Smoke  troubles  in  London 50 

Soot— not  injurious  to  health 42 

Tests  in  England 47 

Steam  jets 45 

Cost  of  operating 71 

General  discussion  of 70 

Increase  carbon  monoxide 46 

Increase  sulphuric  acid  vapors 47 

Objections  to 71 

Reactive  in  effect  upon  combustion ...  46 

Sulphuric  acid  in  soot 47 

Sulphur  compounds  in  chimney  gases 47 

Thermal  unit  —  disagreement  of  authori- 
ties concerning 7 

Baltimore 7 

British 7 

French 8 

Underfeed  stokers 61 

Volatile  matter 19 

Composition  of 19,    20 

Wagon  boiler 37 

Wastes  in  the  boiler  room 53 

Water-tube  boilers 38 

Zero— absolute  of  heat  energy 4 


118 


VIA   LT 


THIS  BOOK  IS  DUE  ON  THE  LAST  DATE 
STAMPED  BELOW 


AN  INITIAL  FINE  OF  25  CENTS 

WILL  BE  ASSESSED  FOR  FAILURE  TO  RETURN 
THIS  BOOK  ON  THE  DATE  DUE.  THE  PENALTY 
WILL  INCREASE  TO  SO  CENTS  ON  THE  FOURTH 
DAY  AND  TO  $1.OO  ON  THE  SEVENTH  DAY 
OVERDUE. 


FEB    15  1935 

1  wO\s 

FEB  1  8  1935 

iTrs       t  *•>    ji  -\fo 

FEB  18   1035 

MAR    4    1S35 

^orSZOPA! 

/.O     l^M    ^* 

^-.Vhv'.  iCt 

LD  21-100m-8,'34 

\IL 


YC  48972 


339477 


UNIVERSITY  OF  CAUFORN1A  LIBRARY 


